Editing Stanisław Ulam (section)

==Move to the United States==
In 1935, [[John von Neumann]], whom Ulam had met in Warsaw, invited him to come to the [[Institute for Advanced Study]] in [[Princeton, New Jersey]], for a few months. In December of that year, Ulam sailed to the US. At Princeton, he went to lectures and seminars, where he heard [[Oswald Veblen]], [[James Waddell Alexander II|James Alexander]], and [[Albert Einstein]]. During a tea party at von Neumann's house, he encountered [[G. D. Birkhoff]], who suggested that he apply for a position with the [[Harvard Society of Fellows]].<ref name='VITA'/> Following up on Birkhoff's suggestion, Ulam spent summers in Poland and academic years at [[Harvard University]] in [[Cambridge, Massachusetts]] from 1936 to 1939, where he worked with [[John C. Oxtoby]] to establish results regarding [[ergodic theory]]. These appeared in ''[[Annals of Mathematics]]'' in 1941.<ref name='AJMAA'/><ref name='OXTOBY'/>

On 20 August 1939, in [[Gdynia]], Józef Ulam, along with his brother Szymon, put his two sons, Stanislaw and 17-year-old [[Adam Ulam|Adam]], on a ship headed for the US.<ref name='VITA'/> Eleven days later, the [[Invasion of Poland#German invasion|Germans invaded Poland]]. Within two months, the Germans completed their [[History of Poland (1939–1945)|occupation]] of western Poland, and the Soviets [[Invasion of Poland#Soviet invasion|invaded]] and occupied eastern Poland. Within two years, Józef Ulam and the rest of his family, including Stanislaw's sister Stefania Ulam, were victims of the [[Holocaust]], [[Hugo Steinhaus]] was in hiding, [[Kazimierz Kuratowski]] was lecturing at the [[Education in Poland during World War II|underground university]] in Warsaw, [[Włodzimierz Stożek]] and his two sons had been killed in the [[massacre of Lwów professors]], and the last problem had been recorded in the [[Scottish Book]]. [[Stefan Banach]] survived the Nazi occupation by feeding [[lice]] at [[Rudolf Weigl|Rudolf Weigl's typhus research institute]]. In 1963, [[Adam Ulam]], who had become an eminent [[Kremlinology|kremlinologist]] at Harvard,<ref name='ADAM'/> received a letter from George Volsky,<ref name='VOLSKY'/> who hid in Józef Ulam's house after deserting from the Polish army. This reminiscence gave a chilling account of Lwów's chaotic scenes in late 1939.<ref name='MOLLY'/> In later life Ulam described himself as "an agnostic. Sometimes I muse deeply on the forces that are for me invisible. When I am almost close to the idea of God, I feel immediately estranged by the horrors of this world, which he seems to tolerate".<ref name='OLGIERD'/>
In 1940, after being recommended by Birkhoff, Ulam became an assistant professor at the [[University of Wisconsin–Madison]]. Here, he became a [[United States citizen]] in 1941.<ref name='VITA'/> That year, he married [[Françoise Aron Ulam|Françoise Aron]].<ref name='AJMAA'/> She had been a French exchange student at [[Mount Holyoke College]], whom he met in Cambridge. They had one daughter, Claire. In [[Madison, Wisconsin|Madison]], Ulam met his friend and colleague C. J. Everett, with whom he collaborated on a number of papers.<ref name="ULAM 125-130"/>