(VAR x y z )
(RULES 
        cond(true, x, y, z) -> cond(and(gr(x, z), gr(y, z)), p(x), p(y), z)
        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
        
)