Definition: An unrestricted
grammar (URG) is a quadruple G = (N, T, P, S),
where
• N is an alphabet of nonterminals
• T is an alphabet of terminals, N Ç T = Æ
• P is a finite set of rules
of the form x
®
y,
where x
Î
(N
È T)* N(N È T)*, y Î (N È T)*
• S Î N is the start nonterminal