fac(0,1):-!.fac(N,Nfac):-N>0.M is N -1.fac(M, Mfac).Nfac is N*Nfac.
fac(5,X).
prog.pl:2-3: warning: singleton variables [Nfac] for fac/2 prog.pl:4: fatal error: redefining built-in predicate (is)/2 compilation failed
Standard output is empty
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