change_index() improved.
change_index() improved.

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