(VAR x y )
(RULES 
        cond(true, x, y) -> cond(and(gr(x, 0), gr(y, 0)), p(x), p(y))
        and(true, true) -> true
        and(x, false) -> false
        and(false, x) -> false
        gr(0, 0) -> false
        gr(0, x) -> false
        gr(s(x), 0) -> true
        gr(s(x), s(y)) -> gr(x, y)
        p(0) -> 0
        p(s(x)) -> x
        
)