a production or production rule in computer science is a "rewrite rule" specifying a symbol substitution that can be recursively performed to generate new symbol sequences. a finite set of productions formula_1 is the main component in the specification of a formal grammar (specifically a generative grammar). the other components are a finite set formula_2 of nonterminal symbols, a finite set (known as an alphabet) formula_3 of terminal symbols that is disjoint from formula_2 and a distinguished symbol formula_5 that is the "start symbol".