%query: factorial(i,o). % From "The Art of Prolog" by Sterling and Shapiro %:::::::::::::: %ss8.2 %:::::::::::::: factorial1(N,F) :- N > 0, N1 is N-1, factorial1(N1,F1), F is N*F1. factorial1(0,1). %:::::::::::::: %ss8.3 %:::::::::::::: factorial2(N,F) :- factorial2(0,N,1,F). factorial2(I,N,T,F):- I < N, I1 is I+1, T1 is T*I1, factorial2(I1,N,T1,F). factorial2(N,N,F,F). %:::::::::::::: %ss8.4 %:::::::::::::: factorial3(N,F) :- factorial3(N,1,F). factorial3(N,T,F):- N > 0, T1 is T*N, N1 is N-1, factorial3(N1,T1,F). factorial3(0,F,F).
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