In formal language theory, the Chomsky–Schützenberger enumeration theorem is a theorem derived by Noam Chomsky and Marcel-Paul Schützenberger about the number of words of a given length generated by an unambiguous context-free grammar. The theorem provides an unexpected link between the theory of formal languages and abstract algebra. == Statement == In order to state the theorem, a few notions from algebra and formal language theory are needed. A power series over N {\displaystyle \mathbb {N} } is an infinite series of the form ...