(VAR x y) (RULES plus(x,0) -> x plus(x,s(y)) -> s(plus(x,y)) times(0,y) -> 0 times(x,0) -> 0 times(s(x),y) -> plus(times(x,y),y) p(s(s(x))) -> s(p(s(x))) p(s(0)) -> 0 fac(s(x)) -> times(fac(p(s(x))), s(x)) )