TRS:
 {           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(a(x, y, h()), l)),
            a(h(), h(), x) -> s(x),
           a(x, s(y), h()) -> a(x, y, s(h())),
          a(x, s(y), s(z)) -> a(x, y, a(x, s(y), z)),
           a(s(x), h(), z) -> a(x, z, z)}
 Fail