Schönfinkel

Moses Schönfinkel was a Russian logician active in the early 20th century. He is best known for introducing combinatory logic, a formal approach to computation that eliminates the need for variables in expressions. His work laid the groundwork for later developments in the theory of programming languages and automated reasoning. Schönfinkel's ideas influenced Haskell Curry and became central to the study of functional computation.

In 1920 he published "On the Building Blocks of Logical Calculus," proposing a small set of combinators, notably S and K, from which all computable functions could be derived. The K combinator captures constant functions, while S enables the distribution of application to its arguments. This variable-free approach allows representing lambda expressions through a concise calculus, and it helped motivate later formulations of combinatory logic and its relationship to the lambda calculus.

Schönfinkel is also associated with the Curry–Schönfinkel class, a decidable fragment of first-order logic obtained by restricting to function-free predicates. This class, sometimes called the Bernays–Schönfinkel or effectively propositional fragment, has the finite model property and underpins certain decision procedures in automated reasoning and theorem proving.

Little is known about his later life; his career was shaped by the political upheavals of his era, and he did not leave a large published legacy. Nevertheless, his pioneering work on combinators and decidable logical fragments remains influential in the history of logic and computer science.