1909 – 1994
Stephen Cole Kleene (1909–1994) was an American mathematical logician and a principal founder of recursion theory. A student of Alonzo Church, he made foundational contributions to computability theory, formal language theory, and the metamathematics of intuitionistic logic. His work established core concepts underlying theoretical computer science and the study of the limits of mechanical computation.
Proved Kleene's recursion theorem, a fundamental result in computability theory
Introduced Kleene's T-predicate and the universal function, formalizing the notion of a computable function
Developed the Kleene star and foundational work on regular expressions and finite automata
Established Kleene's three-valued logic (strong and weak) for formalization of partial functions
Authored Introduction to Metamathematics (1952), a standard graduate text in mathematical logic
Turing's thesis is not susceptible to mathematical proof
claimThere is a fundamental tension between treating logical knowledge as a priori and the computational intractability of deciding logical validity.
claimThe universal function u_1(i,x) = g_i(x) for unary primitive recursive functions cannot itself be primitive recursive