Entscheidungsproblem Decision problem Decidability (logic) Church-Turing thesis Computable function Algorithm Recursion Primitive recursive function Mu operator Ackermann function Turing machine Halting problem Computability theory, computation Herbrand Universe Markov algorithm Lambda calculus Church-Rosser theorem Calculus of constructions Combinatory logic Post correspondence problem Kleene's recursion theorem Recursively enumerable set Recursively enumerable language Decidable language Undecidable language Rice's theorem Post's theorem Turing degree Effective results in number theory Diophantine set Matiyasevich's theorem Word problem for groups Arithmetical hierarchy Subrecursion theory Presburger arithmetic Computational complexity theory Polynomial time Exponential time Complexity class Complexity classes P and NP Cook's theorem List of complexity classes Polynomial hierarchy Exponential hierarchy NP-complete Time hierarchy theorem Space hierarchy theorem Natural proof Hypercomputation Oracle machine Rózsa Péter Alonzo Church Emil Post Alan Turing Jacques Herbrand Haskell Curry Stephen Cole Kleene Definable real number