He then undertook doctoral studies, supervised by Jacob T Schwartz, and he was awarded a PhD from Yale in 1956 for his thesis Extension theory of differential operators.
Siya pagkatapos ay undertook ng doktor pag-aaral, supervised by Jacob T Schwartz, at siya ay iginawad isang PhD mula sa Yale sa 1956 para sa kanyang tesis extension teorya ng kaugalian operator.