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Presenting half-baked results in a department seminar
After having submitted my Ph.D. recently, I am working on a first solo paper (without my advisors). I have some interesting results, but, I have difficulty in formalizing some of the mathematical arguments. I tried to send the manuscript to some mathematicians for comments, and they said they will read it when they have time, but so far, apparently, they did not have time.
So, I scheduled a presentation in a local math department seminar. My hope is that, when people come to a seminar, they have more time to listen, and probably some of them will be able to help me.
My concern is that, presenting such half-baked results might make me look unprofessional.
So, my question is: what is the best way to present such results in a way that will encourage interested listeners to collaborate with me, while not creating a negative impression?

Warning: If the ideas are not clear in your head, then they will be incomprehensible to an audience.

What is your field? It doesn't seem to be mathematics.

@henning my field is computer science + economics.

Make sure you are going to the seminar in advance of your presentation, if it is local. That way you can understand their expectation and how they present partially completed results.

I suggest you include some definite results, perhaps from some other project.  In other words, your talk could cover two topics.

Caveat: The following applies to venues where presenting work in progress is accepted, such as workshops or (as in this case) an internal department seminar. Of course, a high-ranking conference is not the right place for anything half-baked.
The idea is to explain at least those aspects very clearly that are not (as) "half-baked", while being honest about those that are half-baked.

Make your research question very clear and explain why it matters. In the worst case, your audience can't comment on any of your half-baked findings, but then they can at least think with you about your research problem.
Describe very clearly your analytical approach. Which methods/models/concepts/theories did you use to attack your problem? Help your audience to think about whether your analytical choices are useful and how they can be used to attack your problem.
When it comes to your findings and their formalization, try to do a good job in their informal ("natural language") presentation. Perhaps you can already break down the finding analytically without going "fully formal". Then explicitly state that your current challenge is to formalize those findings. Show the audience briefly some angles that you have tried and where you got stuck. Explicitly and politely invite your audience to comment on the formalization.

The easier it is for your audience to understand your work, the easier it will be for them to help you with its formalization. This makes their comments more useful. At the same time, the better job you do at explaining clearly what you have done, what you know, and what you don't know, the more professional you come across.
Your goal is to make the audience think: "Hey, this guy has a very interesting and important puzzle. I think he also has a great model that explains it. I guess I should work with him on its formalization."

First, I am not sure what you mean by "half baked result". You have to be very clear about what results you actually have and which you only anticipate.

If by half-baked result you mean "almost proven result", it is still a conjecture and should be presented as such. For a talk you should present results for which you have a clear proof (presenting the proof itself may not be a good idea depending on time and audience). If you have proofs of special cases of your "conjectures" listeners may be interested to collaborate on the proof of the conjecture.
If by half-baked result you mean "results for which you have an informal proof" but no rigorous one, I am not sure, how to proceed. I would say, that a non-rigorous proof may count as "no proof" and the first bullet applies.

In some fields, half baked results are more related to a proposal of a new model, but without any application which might be the validation of the previous model. For example, one add a new term in the action, but is not studying its application and its effects, only derive the field equations, which, from a mathematical point of view, express the main equations, but without any physical effects.


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How do I get "promoted" as a PC member in a conference?
Recently I served as a Program Committee member (=reviewer) in several conferences in computer science. In these conferences, there is a "hierarchy" of reviewers: there are "PC members", "senior PC members", "area chairs", and the "PC chair".
Do I need to do anything in order to "advance" in this hierarchy?  Or should I just wait until some PC chair in the future decides to "promote" me?

I am not sure if this is the same in your field, but in mine (software systems) PC member and senior PC member are actually different roles with different tasks. It's not so much an honour badge to be a senior PC member than being assigned for a different job in the selection process (typically, PC members do most of the reviewing while senior members do less reviewing and more "meta-reviewing", similar to an Associate Editor for a journal). It's also not the case that, once "promoted", you will always remain in that role - every team of program chairs is free to assemble their own PC, and they invite people to the different roles. This often, but not always, includes re-inviting previous committee members.
I know of cases where people who used to be senior PC members were asked to serve as regular PC members in the following year (or not at all). Also, many senior PC members are actually more junior (in terms of academic age or rank) than some of the regular PC members. This has to do with PC composition - you want to have good coverage of all topical areas that you receive contributions in, and of course past performance and the subjective impression (of the PC chairs) of the different people plays a big role as well.

That is all to say that there typically is no defined promotion process between different levels in a program committee. You need to do good work in previous years and gain sufficient notoriety in the community that the next batch of PC chairs sees you as somebody who they trust to oversee the selection of papers in a specific niche topical area.

This is something you should explore with a conference chair. I'm not especially familiar with any "hierarchy" other than "chair" and "member", but suspect that, where it exists, the definitions and requirements differ.
A PC chair, of course has a lot of responsibility, both in organizing the program and in finding other members, It can take quite a lot of time and effort unless you already have a large set of collaborators and others in your field who know and respect you. I assume that position is invited by the Conference Chair.
I also don't know what effect it will have on your professional standing. How is "Senior PC member" a bonus over just "PC member". Both contribute and show activity in the profession. Chair is a step beyond, of course.
But if the Conference Chair of a given conference rotates among a fairly close set of people, then get yourself associated with them and known to them. Offer to help. Offer ideas for improvement, though carefully.  But just saying you want to be more involved will probably be enough. Finding willing people is a major task.

In my field (TCS/ML/AI), there is a seniority difference between PC and SPC, and in some instances tenure cases (at least their service parts) would place some weight on SPC/PC distinctions.
The easiest way of becoming an SPC is to ask: for instance, if you attend a conference, usually the chairs of next year’s conference are announced, approach them and mention that you’d love to be more involved in the next iteration in a more serious capacity.
Another approach is to initiate other activities to show your readiness to be involved. For example, initiating tutorials or workshops.

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"I" versus "we" in grant application
I am writing a grant application as a sole PI, and it is not clear to me whether I should use singular or plural terms. As an example, currently I have a sentence like this:

"Based on previous work, I got to the conclusion that the present approach X to problem Y is inappropriate. Therefore, in paper Z we developed an alternative approach which I plan to pursue further in the proposed research.

The reason for the switches between "I" and "we" is that the conclusion is mine, but paper Z is a paper I wrote with a coauthor, and the plan to pursue this further is again mine alone. While the terms reflect the reality, it seems bad English to switch back and forth between singular and plural.
In usual research papers, I often use "we" even when I am a sole coauthor, since this is convenient and quite common in my field (computer science). However, using "we" in a personal grant application seems inappropriate.
What is a better style for writing sentences such as the above?

My personal rule of thumb is that we (e.g. the project team) share the work and acknowledgements for the produced results, but I (e.g. the PI) propose, plan and manage the project and I am responsible for the delivery of results.

Your paragraph is less informative than, perhaps, it should be. If you give citations for each claim then it becomes clear. Give a reference after "previous work" and "paper Z", etc. Then the I and we is obvious.
I think that readers of a grant application will want those citations, actually. "What previous work...?"
But an "Royal we" is often used as you say, but it would be a consistent usage. And it could sometimes be interpreted as "we = researchers in the field generally"

Sure, in the actual proposal I give citations. I just wanted to focus on the pronouns.

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Presenting in a remote conference via video-conferencing
A paper of mine just got accepted to a computer science conference. Due to personal reasons I cannot fly to that conference. I was suggested to ask a friend who flies there to present the paper for me, but I think it may not be a good idea since the friend might be unable to answer questions. So I thought of a different solution: I can rent a room with special video-conferencing equipment and present from there.
Is this solution common? What should be taken into account to implement it?

You should check with the conference organizers. If this was not allowed explicitly, you would look like an arrogant. I would probably recommend another coauthor to present or I would retract the submission altogether.

Depending on what field your in, it may be common for people to pull out of conferences. In mine, it's practically de rigueur and it is more common in fields where conferences are significantly less important than journal publications. If you are in a field where something like 75% of the people "wrote" their paper on the plane ride there, you demanding added special treatment and time consuming tech set ups on the organiser's part won't play well.

If this was a childcare or an accessibility issue or related from you being in a lower income country, fair game: academic conferences are terrible on all those fronts and we should all demand accommodation. If you just can't be there, well, other people can't be there too. Also, sorry to say, but you'll likely get little engagement via video. Your best bet is to forget the Qs then pre-record, have your friend present, or pull out.

You could ask a friend to help you present a recorded or live presentation through his/her mobile phone/laptop.
You may wish to record a short video of your presentation/demonstration (slides + audio) and upload it to YouTube; include a short URL and a large QR code on the last slide.
You will need:

Permission from the organizers and/or session chairs (be optimistic!)
A colleague/friend who wants to help and can help (e.g., free during your session)
Reliable internet connection (Wi-Fi) in the conference room

If the connection fails, your friend could at least present your recorded video presentation.
For engagement by the audience, it is the quality of your work that matters most: your excellent remote/recorded presetation is likely to be more engaging and better received than an average one presented in-person.
I tried a slightly modified version of this myself with the help of a colleague, and it was - unexpectedly - successful and well-received, and several people watched the online video shortly later.
P.S: When a computer science conference in 2017/2018 works as in 1980, I believe a cultural change is needed. Teleconferencing is smarter and greener solution than requiring physical presence for everyone, and allows wider participation.

I have never seen this done, and only heard of it being done to accommodate very famous people who have difficulties with travel (e.g., Stephen Hawking, Edward Snowden). So I suspect extremely uncommon and that no one will make a special effort to make this possible for you. However, it never hurts to ask; why don’t you email the conference organizers to ask them? Maybe you’ll get lucky and they are open-minded (or ecologically-minded - it’s worth stressing the savings in carbon emissions from the avoided travel) and happen to have the necessary equipment in the venue they are renting.
By the way, when you contact the organizers to ask about this, I also suggest apologizing for asking the question only after your paper was accepted. When you submit the paper to a conference you are implicitly promising to come and present the paper if it is accepted, so it would have been more responsible to ask the question before deciding to submit the paper, and to have a definite plan of what alternative arrangements you would have in place in case the answer was negative.

That is said, sometime the presenter finds only days before the conference that he/she is unable to attend (declined visa, illness, emergencies) after having paid for the registration fees (and travel/hotel bookings) which may not be refundable and not covered by travel insurence.

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Searching for collaborators in a specific university
My university has signed a cooperation agreement with a different university overseas, and we are encouraged to find potential collaborators in that university. I looked at the university's website, but could not find an easily searchable index of the faculty members by their research topics (I can go to the homepage of each and every faculty member and check, but they are very many).
Is there a way to do such a search in a tool such as Google Scholar? In particular, can I search in Google Scholar for papers with certain keywords, with the constraint that one of the authors should have a specific affiliation? Such a search could lead me to a very focused list of potential collaborators.

Hmm, would you take commercial services like "Web of Science" into account? Perhaps they have more search options?

Long term, find a way to visit. Or to attend conferences where faculty from the other university are likely to attend, say by presenting. Set up a meeting at the conference with all such faculty (both universities) invited.

Web of Science can do this to some extent.

Go to Web of Science and search the keyword in "topic".
After getting results, refine by funding agencies and look for the institution you want.

I'm not sure how comprehensive this is, though.

Thanks! But I had to refine by "Organization" rather than funding agency.

There are likely not all that many departments at the other university where possible collaborators could be located. Assuming they are in a part of the world where departments and people have websites, go to the website of the possible departments, and then the websites of faculty in that department. This way, you are not limited by the vagaries of having to find the right keywords to search, but instead get an overview of what people in that department do -- and maybe find someone who is not doing exactly what you are doing but instead could use the knowledge you have because they don't already have it themselves.

 I tried this, but after filtering by department, there are still 100s of different faculty members to search..

@ErelSegal-Halevi, contact one (or a few) of the likelier ones, and ask them to put you in contact with potential collaborators.

It sounds quite strange to sign collaboration agreements without any feeling of what is going on on the other site. Get the text of the agreements. Presumably some discussions on potential collaboration areas were part of the negotiations, contacting the people signing the agreement (and/or the people involved in negotiations) would be the first step. First locally, then (probably through them) their counterparts.
Contact the chairmen of the possible departments over there, they should be the most interested in getting the collaboration go forward. They should be able (and interested) in putting you in contact with potential counterparts.

I think "being on the ground" makes it really easy to find the right collaborator! Find whoever runs a seminar series in the appropriate department (i.e. you're in math, look for an appropriate math seminar) that you'll want to visit and would be interested in giving a seminar talk. Most people will enjoy the ease in planning something that plans itself. Make sure the talk gets advertised to the right other departments, and try to talk to people when you're there. There's a very good chance that whoever is interested in your work will make it to your talk. Otherwise, someone in the audience will tell you who you need to talk to, and you can probably meet them that day and well, it all starts there.


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Is it rude to write in a journal paper "the proof is left as an exercise to the reader"?
Many books, particularly in mathematics and related disciplines, contain sentences like "the proof is left as an exercise to the reader", which actually mean that the claim should be easy to prove for anyone reading until that point.
Can I write such a sentence in a paper submitted to a journal? Or will the reviewers consider it rude to omit a proof in such a way?

It is not rude. If your fear is that the word "exercise" could be seen as condescending to the reader, then write simply "the proof is left to the reader". Personally I think it communicates more to give some, albeit brief, indication of how to prove the claim in question, even if it is just to say "the proof is is similar to the proof of claim X" or "the claim is proved by applying Lemma Z and the known fact that Blah Blah". A reviewer will only be bothered by such a phrase if the omitted proof is really not so self-evident as you imply.

@DanFox: Please consider converting your comment into a full-fledged answer.

For what it's worth, I have heard of people using such a statement because they themselves have not figured out the proof yet and need more time to do so.

a real example : http://stackoverflow.com/questions/12244968/how-to-implement-the-derr-entry-macro-in-guru-of-the-week-32

There are two separate issues here: omitting the proof, and calling it an exercise.
It is relatively common to omit some proofs in research papers. In particular, proofs that are long but routine, or that re-use the same method as other proofs in the paper, are often abbreviated or removed. It depends on the intended audience for the paper, to some extent. You will get a sense of this by reading more research papers. But caution is needed: one of the first places to look for errors in a paper is in results where the proof was omitted!
The question whether to call something in your paper an "exercise" is more difficult. I wouldn't be surprised if some people do it -- but some people don't write very well. The audience for a paper includes your peers, and you are not really in a position to assign them homework. There are other ways to indicate that a proof is easy besides calling it an exercise: "the following theorem follows directly from definitions", "the proof of the following theorem is routine", "the proof of the following theorem is similar to the proof of Theorem 1.3", etc.   Giving a small hint of how to prove the result can make the paper stronger, and it helps any readers who are not experts in the area.

I think it depends on the context: If it is a research paper, it is definitely rude. As a referee, I would return such a paper to the author to fill it in. If it is a review paper or aims at education in math then it’s fine in my opinion. A different story are textbooks with or without exercises, where it is apropriate.

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Before proposing reviewers, should I notify them?
Some journals require the author to propose potential reviewers. Should I just propose reviewers and let the editor contact them? Or should I first contact the potential reviewers myself and ask if they agree?

You can leave contacting the reviewers to the editor. The editor, in any case, may ignore your recommendations for potential (or blocked) reviewers.

I never asked them and never heard of anybody doing so. It’s the journal who is responsible to organise peer review, not you, and they have to and will humbly ask¹ potential reviewers anyway. By asking potential reviewers yourself, you cause the following problems:

Not every reviewer you suggest will be chosen by the editor. For a reviewer who will not be chosen to review, deciding upon your request will be a waste of time.
Even a reviewer who is eventually chosen will waste a little time by responding to the same request twice.
If a potential reviewer declines your request and you do not suggest them, the editor may still choose them on their own (most editors to whom I have talked make a point of choosing at least one reviewer who was not suggested). In that case, the potential reviewer may think that you ignored their wish.
Asking reviewers directly is a first step to breaching the independence of peer review as it opens up the path for manipulating peer review: “Sure I will review your paper [favourably] – provided that you will do the same thing for my next paper.” Some oppose even the mere option to suggest peer reviewers for this reason.
If you know only a limited list of potential reviewers for your paper, removing those who deny your request may make the list smaller than what is requested by the journal. If those reviewers only refuse when asked by the journal, you still did your duty of suggesting sufficiently many potential reviewers (and this may not even be a problem, if the journal requests a list that is longer than the number of actual reviewers).
You waste some of your time by asking the potential reviewers and waiting for their response may delay the actual submission.
If you show your paper to your potential reviewers privately, they have an advantage in the rare case that they try to steal your ideas or commit other dishonesties. By contrast, peer reviewers are often bound to terms of non-disclosure and similar and also the journal serves as an independent register of who had knowledge of the manuscript. This point does of course not apply, if you trust all potential reviewers or published a preprint of your paper anyway.

¹ Except perhaps for some journals with a questionably demanding demeanor.

You should never ask someone as an author whether they would be willing to serve as a referee for your paper.  In addition to Wrzlprmft's issues:

It looks suspicious, like you may be filtering your suggested referees based on how enthusiastic they seem to you.  This could happen even if it's honestly not your goal.  For example, suppose you ask A, who replies "Wow, I can't wait to read it!", and B, who replies "I'm really busy but I could do it if necessary."  If you suggest only A to the editor, are you biasing the process in favor of your paper, or just being respectful of B's time?  There's no clear way to draw the line.
You're putting potential reviewers in an awkward position by making them tell you whether they could do it.  For example, they may feel more comfortable telling an editor that they are too busy or feel the paper is outside their area of expertise, rather than telling you.  They may also worry that giving you this information decreases their anonymity.

I would say that any contact between referees and authors should be minimized. Just mention any potential referees when submitting.
Secondly, my personal experience is, is that referees are chosen from the existing journal's database, regardless whether and how many potential referees are provided. This, on the basis of the types and quality of the referee's reports I received in a number of cases; for example quite poor and obviously not one of my suggested referees, or their response was way too knowledgeable about certain topics to meet the knowledge on those topics of my suggested referees.
And to add to that: I've talked to an editor-in-chief who gave a crash-course in article writing and he said that he would rather not use the potential referees as they are likely related to the manuscript author(s) in one way or another, professionally or otherwise. He told us that he, therefore, never provided any potential referees with his submissions, unless he had to.

Managing the review of the paper, including the contact with reviewers, is the task of the editor in charge. The process should remain as blind a possible. Knowing too much may bias the review.
However I have witnessed some outlier cases:

a researcher I know had trouble with a paper, for which the editor add difficulties finding reviewers, asked me (and somebody else he knew) as a service to review it. I would probably have refused if it were send by the editor only
acting as both an author and a guest editor for a special issue or a book.

You definitely should contact with reviewers, talk to them and then redirect to the editor.

I strongly disagree with this approach. For reasons, see the other answers.

Welcome to Academia stack exchange! This answer is very brief, and doesn't really provide a rationale as to why someone would want to follow this advice. Could you expand your answer to explain your reasoning?

I had the same dilemma, i talked with reviewers, asked them if they agree, and then they had a conversation with editor, it saved editor`s time. If you disagree, its your choice)

The motivations (time savings) you expose in your comments are important to understand your answer. I would suggest to edit your answer accordingly.

@Bertram if you're willing to come back and improve/add-to your answer in response to comments, others will be much more willing to upvote you.


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What to answer an author asking me if I reviewed his/her paper?
Suppose I review someone's paper anonymously, the paper gets accepted, and a year or two later we meet e.g. in a social event and he/she asks me "did you review my paper?". What should I answer? There are several sub-questions here:

Suppose the review was a good one, and the paper eventualy got accepted, so I do not mind telling that I was the reviewer. Is there any rule/norm prohibiting me from telling the truth?
Suppose the review was not so good, so I do not want to reveal. What can I answer? If I just say "I am not allowed to tell you", this immediately reveals me... On the other hand, I do not want to lie. What options do I have?

I would love to see a good answer to this question, especially since I can also see benefits of disclosing the identity: The author might have particular questions about the review that could improve their future work on the topic.

I'd love to tell you, but then I'd have to reject you ;-)

"I can neither confirm nor deny that I reviewed your paper."

@henning Makes no sense: He could just fill you in about what the referee mentioned, and ask you about your opinion.

"I'll keep you in suspense, OK?"

"No, and if I did I wouldn't tell you."

@Karl but only the referee has read and deeply thought about my paper, and my questions might be following up on the comments.

Are you absolutely certain they mean referee, not "review", as in read it? In academics, "reviewing" can mean being the person who provides input as to a paper's suitability for publication. However, that's not its normal conversational English meaning. if asked that, without it explicitly stated otherwise, I'd assume they're asking if I'd read/reviewed the paper after publication. Unless absolutely clear they're asking if I refereed the paper prior to publication, I'd answer something to the effect of "Yeah, I read it in [where published] a year, or so, ago". In other words, deflect.

@henning That implies a very unfriendly attitude in the way of "please tell me rightaway if you have closely read and understood my paper, otherwise i won't bother wasting my time on you". No? Well, what does it matter then if the guy you are talking to is the actual reviewer or not. You think he might, because his reputation and expertise would qualify him. And come on, "only the reviewer" has read your paper? Why did you write it, then? ;-)

"I don't know, i read tons of crap… so propably yes."

Let him/her talk, ask back "why?". This gives you room for thinking

You could say something like

"I am not in the habit of telling people whether I did or did not review their papers, sorry"

or

"I don't feel comfortable answering this question."

Or you could defuse the question with a humorous answer, e.g.

"I would tell you but then I'd have to kill you"

or

"I don't remember, I always take an amnesia pill immediately after reviewing a paper"

or some similar kind of obviously nonserious smart-assery. None of these answers provide any useful information to the asker, and all of them convey some level of disapproval on your part at being asked, making it unlikely that the asker would press the case any further.

1 for humour. It's the only solution that leaves some ambiguity.

Be very careful with humor, especially the first one. While I hope that most people would recognize it for what it is, there's always the exception who will take offense. And if it's someone in your field...

@tonysdg be very careful with humor: also be very careful with a lack of humor, since I for one find that (especially a lack of humor resulting from people stripping away any semblance of humor from what they're saying to avoid any chance that they will ever offend anyone) somewhat offensive as well.

I agree very much with the idea of diffusing with humor.  Bravo!  I disagree very much that "I would tell you but then I'd have to kill you" is humorous.

@RandallStewart thanks for cleverly hinting that you liked my second joke :)

@DanRomik: Let the record show that I enjoy both jokes :) However, I've learned to err on the side of no humor and caution after getting burned a couple of times (though maybe I just have a warped sense of humor).

@tonysdg I understand. I guess to me "getting burned" on rare occasions is not a bad trade-off when weighed against the benefits that humor provides the rest of the time.

These responses only work if you also give the same responses to folks whose papers you truly didn't review, and are known for your consistency, otherwise the contrast between "No I did not" and "I don't feel comfortable answering this question" is pretty much the same as a straight "No" vs "Yes". In practice I've never heard anybody use any of these to mean anything but "My answer is the option that would make this situation as awkward as possible", which is usually pretty easy to deduce. In reality, 90% of the time, all of these provide plenty of useful information to the asker.

@JasonC I think you take life a bit too seriously (and that statement doesn't convey any useful information because I tell it to everyone and am known for my consistency).

@DanRomik Mostly I'm accused of not taking life seriously enough. But here on SE sites, in comments, independent of my attitudes towards life, I try to post what I think is relevant criticism of the answers when I do not agree with them. And I know that if I asked you about three different papers on three different occasions and you said "No", "Nah I didn't review that one", and "I don't feel comfortable answering this question", I'd know exactly which one you reviewed.

I think it is inappropriate of someone to ask you if you reviewed their paper.  As you point out, if you are in a position where you would only confirm if you were positive, and declining to respond implies a negative review, you are essentially forced to confirm unless you explicitly deny being a reviewer.  In fact just having your jaw drop as the question is asked is probably confirmation enough.  So I think the right answer to the question is an immediate Whether I reviewed that or not is confidential, and that's an inappropriate question.
That being said, I'm not aware of rules that would prevent you from acknowledging the review.  As I mentioned in a comment, for conferences I've seen people explicitly unblind themselves in reviews by choice.  If you wanted to acknowledge it, I think you could.  I've occasionally admitted that to someone in the past, but not because the author asked.

Somebody might not be comfortable telling the author that they're behaving inappropriately, especially if the author is more senior.  It's perfectly possible to decline to answer the question without criticizing the person for asking it.

Yeah, @dan_romik had a better answer in that regard.

It may be inappropriate but it’s fairly frequent.

@KonradRudolph, must depend on your circle of contacts.  Once in 30 years for me.

This approach leaks information.  If the author asked me (a non reviewer), I would probably answer confidently and tersely no - not being aware that the review was anonymous.  Who besides reviewers would answer "confidential"?

@emory, most people who review know it is treated confidentially. If someone asked me if I'd reviewed something I hadn't, I'd like to think I'd answer the same way.  But in practice, I'd probably end up saying it's confidential, but no, don't look at me. Then 5mins later I'd second guess my on-the-spot reaction.

There's a principle I go by now that took me a long time to learn, mainly because it involved a lot of unlearning things I'd internalized since childhood:
It's always okay to lie when someone asks you an inappropriate question. And usually it's the best answer, especially if you have it prepared, since the whole point of the inappropriate question is usually to extract information from you involuntarily through your reaction.
As such the best answer is just "no", regardless of whether you did. If you feel comfortable with the power dynamics, you can follow up with something like "You know, really, you shouldn't go around asking people that. If they did happen to be the reviewer, it would put them in a really bad position."

-1. I agree it's okay to lie in this instance (though that wouldn't be the ideal way to handle it in my opinion), but the blanket statement "It's always okay to lie when someone asks you an inappropriate question" feels much too strong and general to be correct. E.g., if someone asks how much money you make, it's okay to state a figure that is double your actual income? Doesn't feel right to me...

I would agree that the best answer to the question asked by the OP is to just say 'No' and move on with life. Nothing good can come of saying 'yes', or any other answer that just invites discussion and likely indicates to the one asking the question that you did indeed review their paper and reject it.

@DanRomik: A couple things: 1) Appropriateness there depends on the context. If it's a coworker trying to determine if they're being cheated, the question is rather reasonable. Likewise if it's a credit application. But if it's just a random person you meet, you don't owe them any answer. 2) Just because it's okay to lie in situations where the question is inappropriate doesn't mean you're obligated to. My point is that someone asking a question does not automatically obligate you to answer it truthfully or in any particular way at all...

...for yes/no type questions and other situations where a refusal to answer often implies one of the possible answers, lying is often the optimal solution for not giving them information. But for more open-ended things a good NOYB might suffice.

"Just because it's okay to lie in situations where the question is inappropriate [...]". Again, you're assuming a premise that I disagree with. If a random person you meet asks you how much money you make, you are of course not obligated to answer, and you have every right to tell them it's NOYB and/or to tell them off for being rude. But if you do decide to name a figure, I think it's ethically objectionable to lie. Yeah, I agreed that lying is sometimes a justifiable response to an inappropriate question, but not always.

@DanRomik: Then we disagree on this. It's not a premise but my answer and you're free to disagree with it.

@R Let's assume that you are ethically right and that is okay to lie in my situation. But it is not enough to lie - I will also have to lie effectively, i.e, without blinking or showing signs of nervousness. To do this, I will have to practice lying.  And I believe that such a practice is not good for the mental health.

@ErelSegal-Halevi: Neither is being manipulated by other people into giving them what they want good for mental health. Learning ways to defend yourself, whether by lying or some other means, is an important skill to have to avoid being caught off-guard.

If one adopts this strategy, I suggest following the "no" with "but of course, since reviewing is supposed to be anonymous, I would say no even if I had". (One could debate whether this compound statement is actually a lie then....) Of course, we have to say this when the answer is really "no" as well!

@GregMartin: My answer already covered that aspect in a way that's less revealing and addressed that whether you want to do this might depend on the power dynamics.

I can't see how lying is the best solution. I also can't see how not answering implies one of the answers.  Unless the answer was I have never reviewed any papers then I would reply with I don't tell people this information whether or not I had reviewed the paper.  As the answer is independent of the what they are attempting to deduce it offers no information to the asker.  If they read more into it then that is their issue.

@user7328408: The ivory tower moralizing is unsurprising, but the statistical fails in this comment thread are pretty shocking. While it might not work on a given person, statistically, whether someone says "no" or "I'm not comfortable answering that question"/"that's confidential"/etc. is almost certainly strongly correlated with whether they reviewed it. You can imagine yourself answering the latter all you want, but most people are much more likely to just say "no" if the answer was really no, and only object if it was yes.

-1 for a boldly stated absolute law which is patently false.  "It's always okay to lie when someone asks you an inappropriate question."  This is rubbish; what's more, it is obvious rubbish.  Nor am I saying it is always not okay to lie, by the way.  The point is you're stating an absolute moral evaluation which is nothing but a fixed idea.

The absolutism in the above comment, together with its emotionality, is quite amusing. " nothing but a fixed idea" -- um, it's a principle learned by one individual from their own experience.

It's not ok to lie about this for multiple reasons. Evading the question or refusing to answer are ok. Lying is justifiable here if the person asking is in a position of power over you, and even then it would depend on the specifics. Lying about this will have potential negative implications before for the person asking but also for you (e.g. "Why did you make X think that I reviewed his paper by denying that it was you? I've had to spend an hour arguing with him about it!")

Suppose the review was a good one, and the paper eventualy got accepted, so I do not mind telling that I was the reviewer. Is there any rule/norm prohibiting me from telling the truth?

I'm not aware of any such rule. You can tell them if you want but I would advise against it.  It just feels weird: is the person trying to set up some kind of coterie of friends who write positive reviews for each other?

Suppose the review was not so good, so I do not want to reveal. What can I answer? If I just say "I am not allowed to tell you", this immediately reveals me... On the other hand, I do not want to lie. What options do I have?

The best policy for answering questions where the possible answers are "No" and "Yes but I'm not allowed to tell you that, so I'm going to refuse to answer, but then you'll know I mean yes" is to just refuse to answer in all cases.  Security agencies call this policy neither confirm nor deny (NCND). You don't need to explain why you're refusing to answer; just be polite and say that you never answer questions about what papers you have and have not reviewed. If the person doesn't accept this, they are being rude and you don't have to keep talking to them.  If you feel you have to keep talking to them (e.g., they're a senior professor in your field and you don't feel comfortable just walking away), you can explain about NCND but, honestly, they already know that and they're being a jerk.

Regarding the friendly reviews... yes, this is a real risk. Sometimes people are allowed to recommend reviewers, who then shill off the author.  A practice that should be banned universally!

@FredDouglis "is the person trying to set up some kind of coterie of friends who write positive reviews." Doubtful. There are many innocent reasons why a person may ask this [e.g. 1. genuinely curious, 2. thankful for a high effort review, 3. interested in a specific comment, 4. want to start a collaboration based on a reviewer suggestion, 5. asking for clarification on an tool suggested by the reviewer for future work etc.]. Obviously this doesn't make it an appropriate question, but it is best not to assume any bad intentions when they could easily be explained by neutral or positive ones.

@WetLabStudent, I was simply saying it happens, and I've seen it. Not that it is the most likely reason.

I agree with 2. If you never wish to reveal which papers you review, then having a personal NCND policy is a good idea, because then you can automatically answer any unwanted question by stating the policy. If you do this immediately when someone asks you such a question, without even stopping to think about what their paper was about, then I think you can indeed manage to avoid giving any information to the requester.

There's a Warren Buffett quote (in The Essays of Warren Buffett) that I think is a good answer:

If we deny those reports but say "no comment" on other occasions, the no-comments become confirmation.

In other words, tell them that your policy is to neither confirm nor deny.

Good quote, but it's worth pointing out that the same idea was already expressed quite well in @DavidRicherby's answer.

Perhaps you should follow the example of  Howard Percy Robertson (known as the 'R' in the famous FLRW, or Friedmann-Lemaître-Robertson-Walker metric used in physical cosmology.)
He was the referee of the famous Einstein-Rosen paper, which was rejected by Physical Review, prompting Einstein never to publish in Physical Review again.
Einstein ignored the referee report, but months later, it seems, Robertson had a chance to talk to Einstein and may have helped convince him of the error of his ways. However, as far as we know, he never revealed to Einstein that he was the anonymous referee for Physical Review. It was not until 2005 I believe, long after the death of all participants, that Physical Review chose to disclose the referee's identity (http://physicstoday.scitation.org/doi/full/10.1063/1.2117822).

An interesting bit of trivia, but I don't see how it answers the question, even indirectly. We don't know whether Einstein asked if R was a reviewer, and if so, we don't know what R's response was.

We don't know for certain, but we have a pretty good idea that Robertson talked to Einstein and helped convince him of the error of his ways, without revealing his identity as the referee. Even if it is not known with certainty, I think it still serves as a useful example to follow.

How awkward! I once had someone tell me that he was the reviewer of a grant I submitted, which was rejected the year that he reviewed it and it was accepted the following year. Although he told me how happy he was that I resubmitted it the following year, it was very awkward.
Is it possible that the person asking the question is junior and doesn't know that this is inappropriate? I think that a polite response about peer review is appropriate, such as: "In the spirit of peer review, I don't like to discuss whether or not I have reviewed specific papers or grants. However, if there is something about your study that you would like to discuss? If so, I'd be happy to talk with you about it!"
This way you can avoid the question, but demonstrate interest in their work. If the person does not know that their question is inappropriate, you also politely inform them that they should ask people about who reviewed their work.

I'm a bit surprised you're so taken aback. I think it's terribly inappropriate to ask, but I don't find it so horrible to volunteer that someone liked your paper or proposal despite its bad fate.  Especially if it later was accepted.

@FredDouglis one of my levelheaded managers once gave me a great tip: he said "at the end of the day, it's just work" implying that it's important not to take the ups-and-downs personally.

Yes, Fred Douglis, in looking at my response, it comes off a little exaggerated. However, I will say that the way that the person approached me and the larger conversation was awkward (and not provided in detail here), even though the comments I included in my response were benign.

I am aware of at least one paper where a referee went out of cover (after the review process of course) and was explicitly mentioned in a later paper:

X and Y thank Z, who as the anonymous referee was kind enough to
  point out the error (and later became non-anonymous).

so it is sure fine to answer truthfully that yes you did review, but only if you wish of course (and most likely if you have been helpful and the authors of the paper responsive).

In CS systems conferences it is increasingly common to have shepherds, who are known to be a reviewer, though not which one. They are acked by name as well.

I'd really love to be in the position to write this sentence in an article: "The authors would like to thank the anonymous reviewers, John Smith and Jane Doe."

To clarify, I meant they don't know which review the unmasked reviewer authored, though it's often easy to guess.

This is a good question...
In general terms, you should not tell him/her, as peer review, unless open (eg in the BMJ), it is by definition confidential.
If you are willing to, but wish to remain on the safe side, check the peer review policy of the journal for which you reviewed the manuscript. If there is an explicit embargo (e.g. 6 months after publication), then you can probably tell him/her.
Consider also that in the era of Kudos and Publons it will become easier and easier to identify peer reviewers.

Isn't the embargo about copyright matters?

@henning Yes, but they might occasionally have a time frame for peer reviewer identity as well.

I am not aware of policies that require the reviewer identity to be confidential and I know reviewers who choose to put their names in their reviews under the rationale that they won't say anything they wouldn't mind the authors knowing they say.   Can you cite a specific example of this?

Embargoes are about posting free-to-access versions of the paper, which has nothing at all to do with revealing who the reviewers were.

Unfortunately, one cannot check the peer review policy when put on the spot by an awkward question.

I suppose that in a year or two you review more papers than just one. Also I suppose that it must have been really good / really bad paper so you can remember it for a year or two.

Honestly, I don't remember what I reviewed year ago.

If you want to discuss the article, you can as what article they are talking about and phrase your answers as "If I were the reviewer I'd suggest..."

This is the answer I would use.  If the conversation takes place at the conference where the paper in question was presented or if I had read the paper in one of the journals I read, then I might comment upon the paper as a member for the audience or as a journal reader regardless of whether I reviewed it or not.

Edit after comments....
I suggest  that in reply you would use the method of deflection - not answering directly.
You could say reply to the question with something like....

I tend to find that if a reviewer wants to be identified they request one or more of their papers to be cited, which makes their identity known. If your reviewer didn't do this or come right out and tell you then they probably want to remain anonymous and I'm not sure I want to help you figure out who it was. Did you get a particularly nasty review?

So I am suggesting

first, that you tell the person that if their reviewer did not reveal their identity then they probably want to remain anonymous.
secondly, that you say you don't want to help them figure out who it was because if you say 'no, not me' then they will have a smaller group of people to hunt through
thirdly, you ask if they got a really nasty review and if that is why they are asking.... this may lead on to a more general discussion about reviewing

Please note
I do not reveal my identity in reviews by asking for my papers to be cited--- but on several occasions i have seen reviews were people have asked for their papers to be cited.
Original brief reply
Deflection....
You could saysomething like....

I tend to find that if a reviewer wants to be identified they request one or more of their papers to be cited, which makes their identity known. If your reviewer didn't do this or come right out and tell you then they probably want to remain anonymous and I'm not sure I want to help you figure out who it was. Did you get a particularly nasty review?

I disagree with this comment. If a reviewer likes to make her identity known she should just do that. The reviewer should only ask for a citation of their papers, if this really is helping to improve the paper. Quite often as an anonymous reviewer I recommend other people's papers because they did some highly relevant work, and this would have been misinterpreted following your logic. Admittedly, if you suggest citations to your paper, you will often be suspected of being the reviewer.

I agree with @frederik, you ask for papers to be cited because they are relevant, and not for self-promotion, if you are an ethical reviewer. I hate to recommend my own papers and set a much higher bar to mention my own than those of others.

@frederik --- I agree with you, and I did not want to suggest that people should reveal their identities in this way - it is just something that I have seen happen - I have editted my answer to make it clearer - I hope this makes sense now - sorry for any confusion

@ZeroTheHero -- I agree totally, but sometimes people have revealed to me when they have been referees for mine or other people's papers. I do not endorse this, --- I have editted my answer and I hope this makes clearer what I meant

@FredDouglis I agree, I hate to mention my own papers and if I had to would probably mention several with different authors that would be relevant in the area to hide my identity. -- I hope my edited answer is clearer... I do not endorse selfish citation requests in reviews.

But you're still saying that people tend to ask for this, aren't you? With the "you could say" part?

@FredDouglis In my experience I have seen this happen - I am not endorsing it, just saying that it happens...   the point of the answer is to open a disucssion with the person and point out that if the reviewer that they want to track down didn't identify themselves then they probably want to be anonymous.  .... And I am also saying that if reviewers want to be identified they can do this by asking for their papers to be cited. Most of the time reviewers prefer to remain anonymous and do not request paper citations...

We're beating a dead horse, but I strongly disagree with the point that if people want to be identified they'll cite their own work. If they want to be identified, they'll sign their review as some do.

@FredDouglis fair enough

Why don't you say something like "a lot of people ask me that, and I don't tell anyone whether or not I did".  And if you read their paper and liked it or had questions about it, you might as well tell them that, since it's an easy segue into a more productive conversation.


text:
When giving a seminar talk, should I sit or stand?
When I give a talk (e.g. in a department seminar) it is more convenient for me to sit down, since my body is more relaxed and it is easier for me to concentrate in the talk.
But, I have been told that sitting down makes me seem less serious, and it is more professional to stand up while talking.
So, is it better to sit or stand?

With a large audience, standing makes it much easier to project your voice and be heard (singers usually stand up for the same reason). Though I guess in most such cases you would have a microphone anyway.

My discipline always stands. But I have seen academics in other disciplines sit. So it does depend on your discipline.

If there is a reason for you to sit, for example if you can't stand for long periods, and it's not a very formal talk, could you sit on a tall stool, with nothing in front of you? This preserves the difference between you and the audience a bit more than sitting at a table, and also avoids some issues with sitting behind a table (e.g. appearing crouched, audience unable to see your body, seeming less open)

@Roland I'm told that conventions at the time were different: the speaker sat, the audience stood.

I'd like to add that as a deaf person, I rely on people standing up. I need to lipread and for that I need to see your face. Sitting down oftentimes means sitting behind a screen or some other piece of furniture (even if unintentionally).
Just to consider the accessibility aspect as well.

Standing is definitely appropriate in this situation and will help you by increasing your volume, tone, and command of the audience. It seems your preference for sitting may be due to a nervousness in front of an audience.

I am quite nervous even if speaking in front of a small group of well-known and friendly-inclined people. Standing or even stepping around a little helps a lot to dispel the jitters...

@Roland Remember that Socrates et al. didn't have a microphone.

I personally find that sit vs. stand strongly depends on the degree of formality and interactivity of a presentation.

When the presenter stands, it signals a strong differential between the roles of presenter and audience (who sit).  This generally creates a much more formal atmosphere and means that the audience will not contribute to the discussion except to ask occasional questions.
When the presenter sits, it signals a more equal discussion environment, where it just happens that the presenter is the one who is structuring the discussion and/or controlling the slides.  I almost never see this except in the most informal sorts of meetings within a project or group, but in such meetings (e.g., coordination of a project team) it is very common.

For the specific case that you give, of a department seminar, I would strongly advise standing.  The reason for this is that, even if it is a fairly intimate and informal group, a strong motivation for the organization of such seminars is to give you practice for more formal talks.  You may find it more comfortable to be sitting but this is a good opportunity to practice and find ways to be comfortable when standing as well.
Two caveats to all of this:

If a person has a medical condition, they should take whatever position the medical condition encourages.  I've stood and walked around at the back of a talk when my back was having issues; nobody expects Steven Hawking to stand and speak.  If the condition is not obvious, you may wish to inform the audience so they know not to misinterpret your position.
If you are giving a presentation remotely, the position that you are in generally does not matter, as a well-adjusted camera will typically only pick up your head and shoulders.

I agree with this difference - I've had great success with workshop-type environments, where discussion is encouraged, where everybody sits around a table and we simply pass the projector's VGA cable from one to the next. This is very different to (for instance) a conference presentation when one wants to control the room.

I've found that one can encourage some greater informality, interaction and accessibility when standing, by not having a lectern (or other barrier) between me and the audience. Even walking around between the members of the audience (people don't like to have to turn around to see you though). Interaction can be further encouraged by having one or two questions that can be put to some member(s) of the audience (as opposed to general rhetorical questions) without putting that participant under pressure to give the "right" answer.

I have never seen anyone sit down to give a seminar talk (or even a lecture that I can think of), it would come across as extremely unprofessional (unless there were some sort of issue that restricted the ability to stand).
Your ability to feel relaxed and to concentrate on the talk should not be an issue: your talk is prepared ahead of time. What is important is your ability to interact with the audience, to command their attention and to draw them in to your presentation.
I don't think there is any question, and indeed, people have told you that you should stand; so stand.

I had one lecturer who sat for lectures - it was a small class, so it wasn't a problem.

I have seen people give seminars while sitting, but they were not good. Standing helps the speaker engage with the audience.

I remember attending a mathematics conference.  One lecture was presented by John C. Oxtoby.  At that time (because of muscular dystrophy, I guess) he was confined to a wheelchair.  But for his lecture he managed to lever himself out of the chair using crutches; lock the knees of his leg braces; and deliver the lecture while leaning against a pillar.  (He had an assistant writing the appropriate things on the chalkboard as he spoke.)
He clearly thought standing was the proper way to do it.  And I doubt your difficulties in standing are greater than his were.

As the others said, it is circumstantial. In my experience so far a proper talk/presentation should be held standing up. The fact that you are standing itself should get you in the situation where you should automatically remember all the things that you should do in a talk (look at audience, speak loud and clearly, don't talk to fast etc.).
If you just want to present some results on a few non-formal slides, sitting down is okay and standing up might even look a little too stiff. But in the end you should observe or ask what the others do and adjust to that.

I think it's about preference. It's impossible to say one way or the other is right or wrong. It's better to be prepared and to know exactly what you are trying to do and communicate. What is the benefit of looking more serious and professional by standing if your talk is unclear and lacks direction? In addition, what is wrong with looking less professional and serious by sitting if you deliver an exciting and clear message that the audience finds riveting?

+1 The quality of the talk is more important than the look of the presenter.

Only in theory. You can have Albert Einstein up there, if he's dressed like a bum sitting in a bath-tub people won't take him seriously. Presentation is as important as content.

I thought the question was about standing or sitting? I don't recall anything about physical appearance or hot tubs

@RidIculous I feel you are using an extreme example and proving the opposite of your claim: That extremely improper presentation can be a detriment to your content. That, however, says little to nothing about the difference in effect between a 'neutral' or 'proper' presentation on the content.

The example I gave was to be taken with a sense of humor or an understanding of sarcasm. Lacking this the premise of my statement is exemplified in the last sentence: "Presentation is as important as content." It's anybody prerogative to believe differently of course. But Considering the proven effects of eg advertising or marketing I believe this to be a rather naive viewpoint.

-1 Your body and your face are means of communication and an additional channel you can use to get your message across. The medium is the message.

As a mathematician who has attended several philosophy lectures and seminars, I think this depends to a great extent on the discipline. I have never seen a mathematics talk delivered seated, while most philosophy talks I have seen were given by a seated speaker; occasionally, and particularly for bigger lecture rooms, the latter have been given by speaker standing at a lecturn. This most likely stems from the fact that in maths there is typically a lot of detail (notation, definitions, assumptions, results) to be stated more or less precisely and referred to later by the speaker or audience. Much writing or referring to slides follows from this requirement, which is not easily done while seated and facing the audience.
On the other hand in my experience of philosophy talks, the speaker typically reads or talks around a set text such as a written essay, so there is little if any need to write on or refer to a blackboard or projected slides. This leaves the speaker with the option of being seated while giving the talk.
I have never detected any suggestion that a talk was considered less serious or professional for being delivered seated.

You should do what is expected, which in my experience is always to stand, but perhaps is different in other contexts.

When you stand and present you focus the audience on you - your speech and your gestures having the slides and other material as a support for your speech.
When sitting, you focus the audience on the slides, video, etc. putting yourself in the background. It can be understood that your slides are self-explanatory and you are here just to comment it if it is needed.
If you want to actively present yourself and your work, stand. If you want to hide yourself, sit. If you sit down during your speech you are saying "And now I'll show you awesome video!" without any word actually said; when you stand up you are saying "Show is over; listen to me now."

Thus far I've found it depends greatly on your field. In some (Such as Media Studies), the sitting/standing difference comes baked in with the difference between a seminar or lecture structure. You would not be expected to stand during a seminar except for utility purposes.
On the other hand, in the 'suit fields' (business, law) you'd be expected to stand for both types of talks.


text:
Should I change the format of preprint before publishing it as a working paper?
I submit a paper to a journal which allows to publish the preprint as a working paper. After submission, I thought I can just take the version I just submitted and publish it on ResearchGate. But then I thought that it might be problematic to use the same format I used for submission, since then everyone knows to what journal I submitted (or at least, to what publisher). Then, if my paper gets rejected, everyone knows that.
Is this an important consideration? Is it important to change the format of the paper before putting it in a preprint archive?

Personally, I wouldn't bother changing the format.  As a wise colleague once told me, if you aren't getting some papers rejected, you aren't submitting to good enough venues.  If you're proud of the work, there's no need to try to obfuscate where it's been submitted.

You have no need to change the format of the preprint. Although you may not upload it in the publications section in RG, you may as well do so in the unpublished work section.


text:
Inaccurate equations in slides or posters
In a paper I am presenting, a key equation contains the term $1 / floor(n/k)$, where n and k are some integers. This term is quite cumbersome, so I thought that, when I present my paper in a poster or slides, it can be better to present it approximately as just $k/n$.
My questions:

Is it desirable to simplify equations in this way in slides or posters?
What is a simple way to convey the message that the equation is not entirely accurate?

Why is it so cumbersome to write ⌊a/b⌋ rather than a/b?  It adds very little.

I'm having a bit of trouble with the computations here. floor(3/5) is zero. Also floor(7/5) is 1 and the reciprocal isn't likely to be 5/7 without some explanations. You may be confusing people more than helping them. However, the general advice in the answer (https://academia.stackexchange.com/a/112231/75368) seems sound.

"Assume without loss of generality that n is a multiple of k."

The problem with dumbing things down too much is you can attract hecklers who will think your cute little intuition-building model is all there is (no matter how much you emphasize that it isn't), then argue with you that your approach is too simplistic to work. Research is full of arrogant jerks just dying for opportunities to do this. In my experience, it's better to keep things accurate even if that makes it more opaque.


text:
Best cloth for a poster
I am printing a poster for presenting at a conference. I would like to print on cloth so that I can carry it easily in the suitcase.
In many print shops I have to select which cloth exactly to print on. There are many kinds of clothes: satin, canvas, flag, net, etc...
Which material both allows a high printing resolution (so that the details are clearly visible), and remains good-looking after transporting it in a suitcase?

choose a material with a fine weave ie highest number of threads per inch...

I feel like the print shop is in the best position to advise you on that

@LyndonWhite most print-shops I asked mainly produce posters for advertisement outdoors - the considerations for such posters are quite different than for an academic poster.

I always use canvas. My experience says it is great to fold, carry and fix in the board. The printing quality is also excellent, even Arial 10-12 point font size looks very clear in the graphs. Moreover you can fold it in any form. I always make a square/rectangular fold and carry it in my backpack. It never erase any printings. Hope this helps.

Polyester that is dense and supports bright colors is great. I've posted a bit about cloth posters here -- see especially the "update" at the bottom, which notes the excellent "performance knit" fabric from Spoonflower.


text:
Is it good to have slides that may be skipped during a presentation?
I am preparing a seminar talk. Currently the presentation contains some theorems and some proofs. Probably, I will not have time to explain all the proofs - I will have to skip some of them. My question is, which of the two options is better:

Keep the slides with the proofs visible, and during the presentation, if I see that the time is tight, rush through them saying that "I skip the proof", or -
Keep the slides with the proofs hidden,  and during the presentation, if I see that there is enough time, unhide and go through them?

The advantage of option 1 is that the audience sees that I have a proof and they can read it later if they want; also, if I have time it is easier to present the proof;
the disadvantage is that it might look confusing or unprofessional to rush through slides. Are there other considerations?

Yes: it will look unprofessional to rush through slides.  Rule of thumb: The talk always takes longer than you think it will.  Halmos' advice: a mathematics talk should contain at most one proof.

This is not an answer to your question, so I put it as comment: slides.com, and I'm guessing some slides creating application, allow you to organise your slides in two dimensions, which then allows you to skip slides without anyone noticing.

I wouldn't call it unprofessional (unless you are constantly flipping around and make yourself look like a lost and unprepared mess) but it generally is disorienting to show slides you don't explain, and hence is advised against. But what is more important to you, maximizing audience comfort in and retention of material, or impressing them with your research achievements?

Closely related: Should the slides in a presentation be self-explanatory or be as minimal as possible?

Personally, I hate it when the speaker has one thing on the slide but speaks about another one. My attention tends to switch between the two and I might end up not understanding either one. If you are not planning to explain the proof, then don't show it on the slide.

"if there is enough time" for proofs?!? You should practice your presentation so that you time it close to the time allotted. Thus you should know how long your presentation will take. There is usually a defined time for Q&A's  after the presentation.

Agree with @MaxW: check the presentation format. If it is presentation then Q&As, then you should practice your presentation several times to make sure you are as close as possible to the time allotted. It also helps make sure you're as clear as possible and not fumbling for words (which in turns helps you say more things in the allotted time). You could then have spare slides at the end of the presentation for details if questions arise. If questions can be asked during the presentation, then it could be more of a problem.

Short comment (not an answer): almost every presentation I've attended has too many slides with too much on each. I try not to do that in mine.

@MaxW in seminar talks I prefer to be more flexible with Q&A, I let people ask questions whenever they want. So it is not possible to know exactly how much time it will take.

Put the slides that contain the proofs after the last slide and have links on the relevant slides so you can jump to the proof slide and back to the next one.
That way no-one will know if you skip the proofs, but they could see you click the link to jump to a proof if you have the time.

That also works well if there is insufficient time during the presentation, but you get asked about the proof during questions.

Yes, always good to have the extra slides ready after your closing one - proofs, other references etc etc

Zongker, D. demonstrates this invaluable technique.

@PatriciaShanahan As illustrated at 3:38 of this famous talk.

@Kevin came here for exactly that comment

This 'trick' is often used during PhD defences, for instance. Basically you prepare some more in-depth slides about topics that your jury might ask about. Then, when the questions come, you already have an answer ready.

I use a 2D layout for that.
I do not know the software you will be using, with reveal.js you can have a linear progression, and some slides can go "down" (these are the detailed ones).
This way I get to keep the continuity of the presentation, and move deeper if needed.

I guess LaTeX/Beamer offers something similar.

@user2768: I've also seen it in other software (prezi I think) and it is a shame that PowerPoint and Google Slide all follow a linear structure, instead of having a multi-level one (2 directions is good, having a whole tree would be better)

@user2768 If it does, I have never seen it. You can put clickable links from one page to another one (for instance, Beamer shows some navigation symbols by default), but not have more than two navigation keys, as far as I know. And I guess it's a feature that would require some support from the pdf reader to work.

@FedericoPoloni Overlays will get you started.

While I love the answer from Solar Mike and the comment from GEdgar, I'd like to offer an alternative that has sometimes worked well for me:
Occasionally I elect to present a very rough sketch of a proof on my slides--this allows me to show that the proof exists and give some sense of the tools required without getting mired in the intimate details of the argument or burying my audience in a hail of notation.  Depending on how time is running I can either breeze through this sketch quickly or more slowly fill in some of the details and intuition verbally (though I would highly recommend against attempting to present a full proof in this way).  In addition, I can also mention that I would be happy to provide the full proof to anyone who would like to see it.

Keep the slides with the proofs visible and explain -- upon reaching the first proof -- that you've included proofs for those that like to read ahead and you won't have time to go through them/all of them.

Response to DVSA:

That's terrible advice imo...there shouldn't be anything
  on the slides you aren't talking about...skipping the proof [looks] unprepared...

For every speaker there exists an audience member that is unengaged, because they've already understood the material. That audience member can engage themselves with the proof. By explaining, "I'll explain the general idea of the theorem; the proofs are included for those that like to read such details," your criticisms don't apply. This strategy will be appreciated by some often neglected members of the audience.

@DVSA It's excellent imo. (Can we please keep comments -- not just here, throughout this site -- positive?) I'll respond above.

@DSVA You're assuming this approach will "turn attention away from [a] presentation," I contend it will draw attention to the presentation by engaging more of the audience. (Again, please be constructive. E.g., rather than saying "[go] against everything a good presentation is about" -- which is false, since it cannot go against everything -- say what it does go against.)

If I need the high-level explanation, showing the full proof makes me skip around the slide as I try to link your words with the slide contents. If I don't, the proof can distract me while you give an overview but...it's actually distracting me. I won't know when to stop tuning you out and start paying attention to your words again, and will get lost as you move on.  I may also think I don't need your explanation, only to realize, midway that I really do.  On paper, you can easily flag remedial/advanced material and the reader can jump forwards or backwards, but this doesn't work live.

@Matt If you need a high-level explanation, then there's no need for you to read the proof. That can be explained to you. If you ignore that explanation, then that's your responsibility.

In principle, sure: it would be great if everyone of every level got something out of every slide. In practice though, this is exceedingly hard, verging on impossible, to pull off. People who don't "need" to read the proof will, people who shouldn't zone out will. Put another way, the split-the-audience approach will maybe engage a few more people a bit more, but also incurs a huge risk of losing broad swaths of the audience altogether. Furthermore, people are usually much happier to nod along with things they know than stare at the presenter in confusion.

I might(!) consider this approach if I knew the audience was very starkly split between beginners and experts, or if the presentation was mostly meant to be viewed as a recoding, but otherwise I think it's a huge "risk" for very little gain, as DVSA argues above.  If you've got an example of someone successfully pulling this off though, I'd love to see a youtube clip or something.

I can confirm it's been pulled off successfully, but there's no video

@DSVA It works just fine if you plan to publish the slides after the talk, and don't wish to have more than one version floating around. This is quite common in the conferences in my field.

Don't ever say during your presentation, "because we're short on time, we're going to skip these next slides".  That just highlights your failure to prepare a talk that is of the appropriate length, and annoys the audience by teasing them with content that they will not get a chance to see.
If you must prepare some extra slides, either because you don't know in advance how much time you will get, or how many questions the audience will ask, or how interested the audience will be in the technical details, then do it as professionally and seamlessly as possible.
One way is to use Keynote, in which case you can use an iPhone as a remote to control the slides.  The iPhone will display a thumbnail of each slide, which lets you select the slide you want to advance to, and the audience will never know that you skipped anything.
Alternatively, set up the computer such that the external display is not a mirror of the laptop's screen.  That could also let you select the slide from your computer without letting the audience see your supplementary materials.

I, for one, don't think it's annoying to see that there is more material that the speaker can fit in the allotted time. If I really am interested, I can ask them for their slides after the talk. And I don't usually hear other academics complain about it.

Depends on the size of the audience and/or your ability to “read” them.  You figure out in advance what to minimize if you sense they are following well or even bored; and what additional detail to go into if you sense they need it.

The most frequent reason I see for speakers skipping slides is that they were interrupted by questions and were suddenly under time pressure.
Of course, one can naively say "don't accept questions".  Stuff happens.  If an interviewee for a slot refuses to take an important question, that's it for the candidate, and they may as well stop.  You may have a poor session chair that loses control.  Again, stuff happens.  If you insist, under such cases, to stick rigorously to your stack, you're being rude to other in the session, or you look unaware of the situation.
The best speakers need to be able to think on their feet.

Additionally, one of the most common reasons I've seen for getting questions is a presenter trying to gloss too quickly over a slide.

I wouldn't do this in a professional business environment, but for academia it's no big deal to skip slides.
For a seminar talk you will probably have differently formatted handouts, but in any other case it's common to hand out the slides and so they should be linear structured, not 2d or having half of the content in the appendix.
Sure you could try to estimate exactly what you will be able to present in the timeframe, but actually you can't. Your audience should learn something and so they should ask questions if they don't understand something. And based on how many questions there are you will not get anywhere near what you estimated.
I think the ability to adapt your talk to the audience to enable them to get the most out of your talk is far more important than to have a smooth, perfectly planned out show. On the other hand it's more likely that nobody asks questions, only very few can follow up to the last slide, but everybody sits there quite and politely. But that's not how it should be.
The difference to business scenarios is, that it's far more involving for the audience to understand proofs, than to grasp some facts about products and bar charts. And your not trying to sell anything so you don't have to keep a polished facade that might deteriorate by skipping around your slides.

That's curious. I don't think I've ever seen handouts for a seminar... In which fields does this happen in your experience?

@Anyon Computer science is my field of experience. Also includes a lot of proofs

I strongly disagree that this is okay in academia and even more vehemently disagree that you can't reliably make a presentation that fits in a designated timeframe (for any field).
You can, of course, gloss over details to make up time, or go into more detail if you're somehow running way ahead, but both should be as seamless as possible, which mashing the right arrow while saying "And we don't have time for that" is not.

@daign I see, thanks. It makes sense to do it for proofs, I suppose. Also, "see the paper for details" might not work as well in a field with mostly short conference papers.

Some softwares have been suggested to help you skip slides without the audience noticing. I have two options for you in this regard, one is https://prezi.com/ which I have used a fair bit. It allows you to move in any direction between your 'slides' and the other, assuming you are working in PP, is to use 'action' buttons as links to other locations in your presentation (under links tab).
The drawback with both is that you need a thorough knowledge of your presentation, inside, out, back and forwards, as this is how you will be able to move through it!
Some people have complained that the transitions in prezi, very forwards/backwards and fluid, leave them feeling a little sea sick from watching.
Overall, its not a problem to skip slides as long as you cover all the evidence in different ways, such as talking ad-lib with another slide if its appropriate. There is no point in making people suffer the same information twice as that leads to the well known phenomenon of 'death by powerpoint'...

As an addition to the existing answers, if there are slides that you visibly skip over, you should explain why you're doing that. From personal experience, if the audience thinks you're trying to hide something, the whole atmosphere of the presentation can become antagonistic.