His level of research activity throughout his career had been higher than most mathematicians could imagine, and perhaps because of this he effectively gave up research during the fifteen years of his retirement.
Kanyang antas ng pananaliksik na aktibidad sa buong kanyang karera had been na mas mataas kaysa sa karamihan ng mathematicians ay akala, at marahil dahil sa ito siya epektibong gave up ng pananaliksik sa panahon ng labinlimang taon ng kaniyang pagreretiro.