(VAR c x y z )
(RULES 
        plus(0, x) -> x
        plus(s(x), y) -> s(plus(x, y))
        times(0, y) -> 0
        times(s(x), y) -> plus(y, times(x, y))
        exp(x, 0) -> s(0)
        exp(x, s(y)) -> times(x, exp(x, y))
        ge(x, 0) -> true
        ge(0, s(x)) -> false
        ge(s(x), s(y)) -> ge(x, y)
        tower(x, y) -> towerIter(0, x, y, s(0))
        towerIter(c, x, y, z) -> help(ge(c, x), c, x, y, z)
        help(true, c, x, y, z) -> z
        help(false, c, x, y, z) -> towerIter(s(c), x, y, exp(y, z))
        
)