A
Post canonical system, as created by
Emil Post, is a string-manipulation system that starts with finitely-many strings and repeatedly transforms them by applying a finite set j of specified rules of a certain form, thus generating a
formal language. Today they are mainly of historical relevance because every Post canonical system can be reduced to a
string rewriting system (semi-Thue system), which is a simpler formulation. Both formalisms are
Turing complete.