(VAR x y )
(RULES 
        nonZero(0) -> false
        nonZero(s(x)) -> true
        p(0) -> 0
        p(s(x)) -> x
        id_inc(x) -> x
        id_inc(x) -> s(x)
        random(x) -> rand(x, 0)
        rand(x, y) -> if(nonZero(x), x, y)
        if(false, x, y) -> y
        if(true, x, y) -> rand(p(x), id_inc(y))
        
)