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Leon Henkin (19 April 1921–1 November 2006) was a logician at the University of California, Berkeley. He was principally known for the "Henkin Completeness Proof": his version of the proof of the semantic completeness of standard systems of first-order logic.

Contents 1 The completeness proof 2 Early life 3 Academic career 4 Awards received 5 See also 6 References 7 Notes 8 External links

Henkin's result was not novel; it had first been proved by Kurt Gödel in his doctoral dissertation which was completed in 1929. (See Gödel's completeness theorem. Gödel published a version of the proof in 1930.) Henkin's 1949 proof is much easier to survey than Gödel's and has thus become the standard choice of completeness proof for presentation in introductory classes and texts.

The proof is non-constructive (a pure existence proof): while it guarantees that if a sentence α follows (semantically) from a set of sentences Σ, then there is a proof of α from Σ, it gives no indication of the nature of that proof.

Later, Henkin generalized this result to a variant of Church's higher-order logic. This variant uses general models (also called Henkin models): the higher types need not be interpreted by the full space of functions; a subset of the function space may be used instead.

He was born in Brooklyn, into a Russian Jewish immigrant family. His first degree was in mathematics and philosophy from Columbia College, in 1941. He took a master's degree there in 1942.

He then worked in the Signal Corps Radar Laboratory, Belmar, New Jersey. As participant in the Manhattan project, he worked on isotope diffusion, in New York, and Oak Ridge, Tennessee.

He was a doctoral student of Alonzo Church at Princeton University, receiving his Ph.D. in 1947. He became Professor of Mathematics at the University of California, Berkeley, where he had a position from 1953. He received the 1964 Chauvenet Prize for exposition.[3] He was a collaborator of Alfred Tarski, and an ally in promoting logic.^[1]

• 2000 - Leon Henkin Citation - for Distinguished Service, which is presented to a (UC) faculty member for "exceptional commitment to the educational development of students from groups who are underrepresented in the academy."
• 1991 - Berkeley Citation - the highest honor/award bestowed by the University of California
• 1990 - First recipient of the Gung and Hu Award for Distinguished Service to Mathematics
• 1972 - Lester R. Ford Award - for Mathematical foundations for mathematics, American Mathematical Monthly 78 (1971), 463-487.
• 1964 - The Chauvenet Prize, Mathematical Association of America award to the author of an outstanding expository article on a mathematical topic by a member of the Association.

• Branching quantifier

• Henkin, Leon. 1949. "The Completeness of the First-Order Functional Calculus", Journal of Symbolic Logic. 14: 159–166.
• Henkin, Leon. 1950. "Completeness in the theory of types", Journal of Symbolic Logic 15: 81–91.

1. ^ Solomon Feferman on Tarski's campaigning [1], [2] explains Henkin's role as recruit and ally.

• Leon Henkin at the Mathematics Genealogy Project
• Berkeley Citation Award
• An interview with Henkin and others about their experiences at Princeton
• An interview with Henkin about his experience at Princeton
• Berkeley press release
• LA Times obituary, November 16, 2006