Introduction to Lambda Calculus
"In mathematical logic and computer science, lambda calculus, also λ-calculus, is a formal system. It was designed to investigate the definition of functions, and how to apply them. It is also a tool for analysing recursion. It was introduced by Alonzo Church and Stephen Cole Kleene in the 1930s. Church used lambda calculus in 1936 to give a negative answer to the Entscheidungsproblem. Lambda calculus can be used to define what a computable function is. No general algorithm can answer the question of whether two lambda calculus expressions are equivalent. This was the first question, even before the halting problem, for which undecidability could be proved. Lambda calculus has greatly influenced functional programming languages, such as LISP, ML and Haskell."
source:
https://simple.wikipedia.org/wiki/Lambda_calculus