▁little - known ▁fact ▁is ▁that ▁during ▁this ▁time ▁he ▁started ▁teaching ▁himself ▁German , ▁Italian , ▁Russian ▁and ▁French ▁so ▁that ▁he ▁could ▁study ▁mathematical ▁works ▁in ▁their ▁original ▁form . ▁His ▁personal ▁library ▁contained ▁quite ▁a ▁few ▁non - English ▁mathematical ▁works . ▁ ▁Ill ness ▁and ▁death ▁ ▁Between ▁ 1 9 6 4 ▁and ▁ 1 9 6 8 , ▁he ▁was ▁making ▁great ▁str ides ▁in ▁number ▁theory ▁and ▁his ▁contacts ▁with ▁Sh af are v ich ▁and ▁M um ford ▁led ▁him ▁on ▁to ▁algebraic ▁geometry . ▁According ▁to ▁Ram an athan ▁and ▁other ▁colle agues , ▁his ▁progress ▁and ▁deep ▁understanding ▁of ▁algebraic ▁geometry ▁was ▁phenomen al . ▁In ▁ 1 9 6 4 , ▁based ▁on ▁his ▁participation ▁in ▁the ▁International ▁Col lo qu ium ▁on ▁D iffer ential ▁Analysis , ▁he ▁earned ▁the ▁respect ▁of ▁Alexander ▁Gro th end ieck ▁and ▁of ▁David ▁M um ford , ▁who ▁invited ▁him ▁to ▁Paris ▁and ▁Harvard . ▁He ▁accepted ▁the ▁inv itation ▁and ▁was ▁in ▁Paris , ▁but ▁for ▁a ▁brief ▁period . ▁He ▁was ▁diagn osed ▁in ▁ 1 9 6 4 ▁with ▁sch iz op hren ia ▁with ▁severe ▁de pression ▁and ▁left ▁Paris ▁for ▁Chen na i . ▁He ▁later ▁decided ▁to ▁quit ▁his ▁position ▁at ▁T IF R . ▁ ▁He ▁quit ▁his ▁post ▁at ▁M umb ai ▁in ▁ 1 9 6 5 ▁after ▁a ▁bout ▁of ▁ill ness ▁and ▁secured ▁a ▁ten ured ▁position ▁as ▁a ▁professor ▁in ▁Ch and