(VAR x y z )
(RULES 
        plus(0, x) -> x
        plus(s(x), y) -> s(plus(p(s(x)), y))
        times(0, y) -> 0
        times(s(x), y) -> plus(y, times(p(s(x)), y))
        exp(x, 0) -> s(0)
        exp(x, s(y)) -> times(x, exp(x, y))
        p(s(0)) -> 0
        p(s(s(x))) -> s(p(s(x)))
        tower(x, y) -> towerIter(x, y, s(0))
        towerIter(0, y, z) -> z
        towerIter(s(x), y, z) -> towerIter(p(s(x)), y, exp(y, z))
        
)