(VAR k l x y)
(THEORY (AC plus))
(RULES
  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)))))
  sum(cons(0, cons(plus(x, y), l))) -> pred(sum(cons(s(x), cons(y, l))))
  plus(0, y) -> y
  plus(s(x), y) -> s(plus(x, y))
  pred(cons(s(x), nil)) -> cons(x, nil)
)