He later made researches and investigations in the United States he went to ; He served as a visiting professor at the University of California . Upon voluntarily want to live in Turkey , he returned to Turkey in 1967 . Shortly after returning , he received offers from universities in Canada and the USA as a visiting lecturer . However , before he could respond to these offers , the phone from the Middle East Technical University said that he was assigned to this university and that the flight ticket was on the way , and he was now in office at the Middle East Technical University . He retired in 1980 . After his retirement , he contributed a lot to the establishment of TÜBİTAK and worked at the Gebze Research Center of TÜBİTAK . He was the president of the Turkish Mathematics Association between 1983-1989 .