(VAR x y )
(RULES 
        half(x) -> if(ge(x, s(s(0))), x)
        if(false, x) -> 0
        if(true, x) -> s(half(p(p(x))))
        p(0) -> 0
        p(s(x)) -> x
        ge(x, 0) -> true
        ge(0, s(x)) -> false
        ge(s(x), s(y)) -> ge(x, y)
        log(0) -> 0
        log(s(x)) -> s(log(half(s(x))))
        
)