static <A> int indexOfLL(L<A> x, A... y) {
  outer: for (int i = 0; i+l(y) <= l(x); i++) {
    for (int j = 0; j < l(y); j++)
      if (neq(x.get(i+j), y[j]))
        continue outer;
    ret i;
  }
  ret -1;
}