He was invited by André Weil to visit Chicago in January 1948, and he received an invitation to visit Harvard University for four months, February to May 1948.
Siya ay inimbitahan ng Andre Weil upang bisitahin ang Chicago sa Enero 1948, siya at natanggap ng isang imbitasyon upang bisitahin ang Harvard University para sa apat na buwan, Pebrero-Mayo 1948.