SKI combinator calculus

The SKI combinator calculus is a system of combinatory logic and a computational system introduced by Moses Schonfinkel and Haskell Curry. It is an extremely simple, Turing complete language built from just three combinators, and it holds an important place in the mathematical theory of algorithms. The I combinator returns its argument unchanged, the K combinator takes an argument and returns a constant function that always returns that argument, and the S combinator, a kind of substitution operator, takes three arguments and applies the first to the third and to the result of the second applied to the third. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/