▁to ▁ 1 9 6 9 , ▁and ▁became ▁an ▁Ass istant ▁Professor ▁there ▁from ▁ 1 9 6 9 ▁to ▁ 1 9 7 2 . ▁He ▁then ▁went ▁to ▁Pennsylvania ▁State ▁University , ▁where ▁he ▁was ▁promoted ▁to ▁professor ▁in ▁ 1 9 7 8 . ▁Later ▁he ▁joined ▁the ▁University ▁of ▁Michigan ▁( 1 9 7 9 – 1 9 8 5 ) ▁and ▁Columbia ▁University ▁( 1 9 8 4 – 1 9 9 2 ). ▁Since ▁ 1 9 9 0 ▁Far rell ▁has ▁been ▁a ▁fac ulty ▁member ▁at ▁S UN Y ▁B ingham ton . ▁ ▁In ▁ 1 9 7 0 , ▁Far rell ▁was ▁invited ▁to ▁give ▁a ▁ 5 0 - min ute ▁address ▁at ▁the ▁International ▁Congress ▁of ▁Mathemat icians ▁about ▁his ▁th esis ▁in ▁Nice , ▁France . ▁ ▁In ▁ 1 9 9 0 , ▁for ▁their ▁joint ▁work ▁on ▁R ig id ity ▁in ▁Ge ometry ▁and ▁Top ology , ▁his ▁co - author ▁Low ell ▁Ed win ▁Jones ▁was ▁invited ▁to ▁give ▁a ▁ 4 5 - min ute ▁address ▁at ▁the ▁International ▁Congress ▁of ▁Mathemat icians ▁in ▁Ky oto , ▁Japan . ▁ ▁Mathemat ical ▁contributions ▁ ▁Much ▁of ▁Far rell ' s ▁work ▁lies ▁around ▁the ▁Bor el ▁conject ure . ▁He ▁and ▁his ▁co - auth ors ▁have ▁verified ▁the ▁conject ure ▁for ▁various ▁cases , ▁most ▁not ably ▁flat ▁manif olds , ▁non pos it ively ▁cur ved ▁ ▁manif olds . ▁ ▁In