(VAR x y z k l)
(THEORY (AC plus))
(RULES
  minus(x, 0) -> x
  minus(s(x), s(y)) -> minus(x, y)
  minus(minus(x, y), z) -> minus(x, plus(y, z))
  quot(0, s(y)) -> 0
  quot(s(x), s(y)) -> s(quot(minus(x, y), s(y)))
  plus(0, y) -> y
  plus(s(x), y) -> s(plus(x, y))
  app(nil, k) -> k
  app(l, nil) -> l
  app(cons(x, l), k) -> cons(x, app(l, k))
  sum(cons(x, nil)) -> cons(x, nil)
  sum(cons(x, cons(y, l))) -> sum(cons(plus(x, y), l))
  sum(app(l, cons(x, cons(y, k)))) -> sum(app(l, sum(cons(x, cons(y, k)))))
)