replaced by b.

In the classic formalization of generative grammars first proposed by Noam Chomsky in the 1950s, a grammar G consists of the following components:
* A finite set of nonterminal symbols.
* A finite set of terminal symbols that is disjoint from .
* A finite set of production rules, each rule of the form
::
:where denotes the set of all possible finite-length strings over the vocabulary using Kleene star.