Gaal later went to
Paris, where he was employed by the
CNRS (Centre National del la Recherche Scientifique) at the rank of
attaché de recherché. His supervisor was
Jean Favard with higher supervisor
Jacques Hadamard. Gaal met many leading French mathematicians at the CNRS, including
Jean Leray and both
Élie and
Henri Cartan. After emigrating to the United States, he held positions at
Yale and Princeton before joining the faculty of the School of Mathematics at the
University of Minnesota.
Atle Selberg was instrumental in bringing Gaal to the
Institute for Advanced Study in
Princeton, New Jersey. While in Princeton, Gaal met
Albert Einstein, though the two did not work together. It also was in Paris that Gaal had first met Paul Erdős. Seven years later, they wrote two more joint papers. Over the years, Gaal met Erdős on a number of other occasions, including his last visit to Minneapolis on the invitation of Carleton College, who sponsored his visit.
Robert Langlands has cited Gaal's influence in his early investigations of
zeta functions and
Eisenstein series. Gaal's former wife,
Lisl Gaal (originally Lisl Novak), is an accomplished mathematician in her own right and is well known for her text
Classical Galois Theory. In 2004, Gaal was honored at the
Hungarian Academy of Sciences 80th anniversary as one of the "big five" most distinguished Hungarian mathematicians. The other honorees included
John Horvath,
János Aczél,
Ákos Császár and
László Fuchs. Gaal gave a talk entitled "When is a Fibonacci sequence periodic?" ==Books==