> quadruple G=(N,Σ,P,S), where T is a finite set of nonterminal symbols, Σ a finite set of terminal symbols, P is a set of production rules and S is a start symbol.

I think "T" is supposed to be "N" in that sentence[1], based solely upon the further use of "N" nomenclature in subsequent paragraphs

1: he said, 5 years too late into a forum just discussing the article