What is the difference between 交易就告成立. and 交易即告成立.? What is the difference between 交易就告成立. and 交易即告成立.?

The catch: Since every book says that 就=即 I considered to create a new sentence out 交易即告成立 by switchin characters.There is no instance of 交易就告成立 have been found by me as of yet. But it should I hope bring the difference between 就 and 即 to the surface.

One native said:


  前者表示已经成立。后者表示还未成立但即将或者很快成立


Some of my reseach:
As far as I know 即 the core meaning is "identity". It seems this character has been merged with 卽(to eat, fast) on the basis of sound and similarity of composition.

Here is the saying from some Buddist book:


  道遠乎哉。即物而真聖遠乎哉 “Is the Way far away? Reality is wherever there is
  identity with things”


即(ji) here is translated as "identical, identity".

another example from some modern manual:


  "CIS即视觉识别系统，其含义是:......"


here 即 again means "namely or identical".

P.S. please, don't tell me it's about food. Or if you do explain how food has something to do with "identity".

P.S.S. IMHO I would say that 即 looks more like a man hunching over tracks on ground 艮+卩. IMHO. IMHO.

P.S.S. Context:


国际商品贸易合同的签汀在交易磋商过程中,一方发盘经另一方接受以后,交易即告成立,贸易双方就构成了合同关系。
在实盘有效期内发盘人受其约束,只要受盘人在规定期限内接受发盘,交易即告成立
...\
P.S.S.S.
From a random guy in the internet: 



  若甲方收到乙方发出的订货单后七天内，未通知乙方其不接受该订货单的订货，则视为甲方确认订货单，订货单所载约定产品交易即告成立
  
  Legally speaking, “即告成立” means that transaction or deal takes effect
  upon the elapse of that seven days.
  
  The wording I propose should be acceptable in most cases for such
  translation.
The only difference between 交易就告成立 and 交易即告成立 is that the former is more used in spoken language and the latter in written language. 即 in 交易即告成立 is a very formal word and functions as an adverb, meaning "right away/at once/immediately/thereupon". When 即 is used in this sense, usually it can be replaced with 就. There is no difference between 即 and 就 in their meanings or grammatical roles in this case. Another example:


  It took the police only several days to break the case. 该案仅几天即告破/该案仅几天就告破(了).


When used in some idioms, for example, 一触即发, 一拍即合, 稍纵即逝, 即 can't be replaced with 就, though 即 still means "right away/at once/immediately/thereupon" in these words.

As for CIS即视觉识别系统, 即 is a conjunction here. In the construction A即B, 即 roughly means "namely/is also called/equals". B explains or rephrases A. It's not the same with 交易即告成立. 就 can't mean "namely/is also called/equals", so it can't be used in place of 即 in this case.

Your native friend may simply base his/her answer on intuition. If you need an exhaustive explanation, you'd better refer to some Chinese grammar books. @user6065 gave a good reference book 汉语800虚词用法词典.

Edit:

I beg to differ with @wpt's claim that the use of 就 in 交易就告成立 is a misuse influenced by dictionary definition.

Here is the definition of 即 in Contemporary Chinese Dictionary, 6th Edition, page 605.



⑥&lt;书>[副] 就;便：一触~发 | 招之~来 | 闻过~改。

&lt;书> means this meaning of 即 is usually used in written language. [副] means 即 is used as an adverb. 

Here, the dictionary used 就/便 directly as the explanation of 即. That's just because 即, 就, 便 all have the meaning of "right away/at once/immediately/something happens soon after another". Except for some idioms and Chengyu(成语), wherever you use 即 in this sense, you can use 就 or 便 in place of 即. The three words are interchangeable grammatically and semantically. As I just said, the only difference is that 即 is more formal than 就 and 便.

There is a paper on the evolution of 即, 就, 便 from verb to function word (adverb and conjunction). cf. “即”、“便”、“就”虚化过程中的错项移植. With regard to when 就 was first used as adverb, the scholars haven't reached an agreement. The author of this paper believes it's no later than Song dynasty (960-1279).

@wpt claimed that 即告 is a set phrase. My opinion is that 即告 is just a commonly used phrase, not a set phrase. Less Google search results doesn't mean 就告 is a misuse. Greater occurrence of 即告 in formal documentatuions doesn't mean it can't be replaced with 就告 gramatically and semantically.