Post correspondence problem - WikipediaNot to be confused with the other Post's problem on the existence of incomparable r.e. Turing degrees. The Post correspondence problem is an undecidable decision problem that was introduced by Emil Post in 1946.[1] Because it is simpler than the halting problem and the Entscheidungsproblem it is often used in proofs of undecidability. Let be an alphabet with at least two symbols. The input of the
