Stanley Tennenbaum (April 11, 1927 â May 4, 2005) was an American mathematician who contributed to the field of logic. In 1959, he published Tennenbaum's theorem, which states that no countable nonstandard model of Peano arithmetic (PA) can be recursive, i.e. the operations + and àof a nonstandard model of PA are not recursively definable in the + and àoperations of the standard model. He was a professor at Yeshiva University in the 1960s.