only combine two-term Add in _invert if a Pow is involved
only combine two-term Add in _invert if a Pow is involved

aktech/sympy,Davidjohnwilson/sympy,AunShiLord/sympy,sunny94/temp,asm666/sympy,vipulroxx/sympy,rahuldan/sympy,wyom/sympy,pandeyadarsh/sympy,wanglongqi/sympy,shipci/sympy,drufat/sympy,skirpichev/omg,hrashk/sympy,wanglongqi/sympy,kevalds51/sympy,shipci/sympy,hrashk/sympy,rahuldan/sympy,VaibhavAgarwalVA/sympy,abhiii5459/sympy,MridulS/sympy,dqnykamp/sympy,lindsayad/sympy,Sumith1896/sympy,flacjacket/sympy,MridulS/sympy,jerli/sympy,sahmed95/sympy,AkademieOlympia/sympy,mafiya69/sympy,emon10005/sympy,chaffra/sympy,iamutkarshtiwari/sympy,jamesblunt/sympy,ChristinaZografou/sympy,toolforger/sympy,abloomston/sympy,cswiercz/sympy,kumarkrishna/sympy,saurabhjn76/sympy,Shaswat27/sympy,yukoba/sympy,Davidjohnwilson/sympy,dqnykamp/sympy,Curious72/sympy,Shaswat27/sympy,skidzo/sympy,madan96/sympy,lidavidm/sympy,AkademieOlympia/sympy,Sumith1896/sympy,aktech/sympy,atreyv/sympy,kmacinnis/sympy,bukzor/sympy,ga7g08/sympy,cccfran/sympy,sunny94/temp,Vishluck/sympy,wyom/sympy,emon10005/sympy,Curious72/sympy,ahhda/sympy,farhaanbukhsh/sympy,Arafatk/sympy,Davidjohnwilson/sympy,kaushik94/sympy,kumarkrishna/sympy,atsao72/sympy,yashsharan/sympy,drufat/sympy,madan96/sympy,srjoglekar246/sympy,postvakje/sympy,ga7g08/sympy,Titan-C/sympy,debugger22/sympy,liangjiaxing/sympy,sunny94/temp,Arafatk/sympy,Gadal/sympy,AunShiLord/sympy,jbbskinny/sympy,liangjiaxing/sympy,kevalds51/sympy,maniteja123/sympy,ChristinaZografou/sympy,pbrady/sympy,cccfran/sympy,maniteja123/sympy,jaimahajan1997/sympy,sampadsaha5/sympy,grevutiu-gabriel/sympy,amitjamadagni/sympy,sahmed95/sympy,asm666/sympy,cswiercz/sympy,lidavidm/sympy,Titan-C/sympy,Arafatk/sympy,postvakje/sympy,atsao72/sympy,lidavidm/sympy,mcdaniel67/sympy,abhiii5459/sympy,kmacinnis/sympy,jamesblunt/sympy,farhaanbukhsh/sympy,jerli/sympy,Sumith1896/sympy,iamutkarshtiwari/sympy,Designist/sympy,jbbskinny/sympy,iamutkarshtiwari/sympy,VaibhavAgarwalVA/sympy,toolforger/sympy,kaichogami/sympy,atreyv/sympy,sahilshekhawat/sympy,maniteja123/sympy,beni55/sympy,abhiii5459/sympy,meghana1995/sympy,amitjamadagni/sympy,asm666/sympy,moble/sympy,Shaswat27/sympy,MechCoder/sympy,emon10005/sympy,oliverlee/sympy,ahhda/sympy,AkademieOlympia/sympy,postvakje/sympy,debugger22/sympy,pbrady/sympy,jaimahajan1997/sympy,yashsharan/sympy,kevalds51/sympy,grevutiu-gabriel/sympy,saurabhjn76/sympy,yukoba/sympy,souravsingh/sympy,liangjiaxing/sympy,mafiya69/sympy,bukzor/sympy,MechCoder/sympy,Designist/sympy,garvitr/sympy,ga7g08/sympy,kaushik94/sympy,sahilshekhawat/sympy,aktech/sympy,atsao72/sympy,oliverlee/sympy,VaibhavAgarwalVA/sympy,shipci/sympy,debugger22/sympy,hargup/sympy,pbrady/sympy,beni55/sympy,sahmed95/sympy,hrashk/sympy,kaichogami/sympy,jaimahajan1997/sympy,kaushik94/sympy,moble/sympy,Curious72/sympy,pandeyadarsh/sympy,abloomston/sympy,shikil/sympy,sahilshekhawat/sympy,bukzor/sympy,jbbskinny/sympy,chaffra/sympy,Mitchkoens/sympy,garvitr/sympy,lindsayad/sympy,cccfran/sympy,Vishluck/sympy,meghana1995/sympy,Gadal/sympy,shikil/sympy,MridulS/sympy,abloomston/sympy,rahuldan/sympy,garvitr/sympy,sampadsaha5/sympy,grevutiu-gabriel/sympy,mafiya69/sympy,skidzo/sympy,mcdaniel67/sympy,madan96/sympy,pandeyadarsh/sympy,Mitchkoens/sympy,yukoba/sympy,souravsingh/sympy,kaichogami/sympy,hargup/sympy,kmacinnis/sympy,souravsingh/sympy,oliverlee/sympy,wyom/sympy,vipulroxx/sympy,drufat/sympy,moble/sympy,Titan-C/sympy,ChristinaZografou/sympy,kumarkrishna/sympy,diofant/diofant,ahhda/sympy,cswiercz/sympy,dqnykamp/sympy,saurabhjn76/sympy,beni55/sympy,Designist/sympy,Mitchkoens/sympy,skidzo/sympy,farhaanbukhsh/sympy,Vishluck/sympy,toolforger/sympy,meghana1995/sympy,jamesblunt/sympy,Gadal/sympy,hargup/sympy,shikil/sympy,MechCoder/sympy,mcdaniel67/sympy,sampadsaha5/sympy,lindsayad/sympy,wanglongqi/sympy,AunShiLord/sympy,yashsharan/sympy,chaffra/sympy,vipulroxx/sympy,atreyv/sympy,jerli/sympy