(VAR x y u v)
(RULES
minus(x, y) -> cond(gt(x, y), x, y)
cond(false, x, y) -> 0
cond(true, x, y) -> s(minus(x, s(y)))
gt(0, v) -> false
gt(s(u), 0) -> true
gt(s(u), s(v)) -> gt(u, v)
)