Codigo Prolog Factorial

domains
Nro= Integer

predicates
nondeterm factorial(Nro,Nro,Nro).

clauses
factorial(Inc,A,X):-R=Inc+1,!,W=A*Inc,write("EL FACTORIAL DE ",Inc," ES ",W),nl,R<=X,
factorial(R,W,X).

goal
write("DIGITE EL NUMERO QUE QUIERE HALLAR EL FACTORIAL "),readint(X),factorial(1,1,X).