Unrestricted Grammar: Definition
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
• Strictly mathematically, P is a finite relation from             (N È T)*N (N È T)* to (N È T)*
• Instead of (x, y) Î P, we write x ® y Î P
Mathematical Note on Rules:
Generalization of CFG
 Gist:
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