:- [pg_with_trace].

article_with_trace :-
	name(FileName, "article_with_trace.pl"),
	open(FileName,write,Stream),
	sigma_pg(pg(f,[f,g],[
	     [(f(0) -> zero), (f(s(n)) -> g(s(n))*f(n))],
	     [(g(0) -> zero),(g(s(n)) -> suc(g(n)))]
	    ]),Stream),
	close(Stream).