static Pair<IntRange, O> findUsingWordTree(L<S> tok, Map<S, O> tree) {

  ret findUsingWordTree(tok, tree, 0);

}

// tok = CNC

// returns (index range C to N, tree leaf)

static Pair<IntRange, O> findUsingWordTree(L<S> tok, Map<S, O> tree, int i) {

  if (tree == null) null;

  O best = null; // best leaf

  int bestIndex = 0; // best index

  int n = l(tok);

  i |= 1; // Proceed to C token

  while (i <= n) {

    int j = i;

    while true {

      O def = tree.get("<default>");

      if (def != null) { best = def; bestIndex = j; }

      if (j >= n) break;

      O t = tree.get(tok.get(j));

      j += 2;

      if (t == null) break;

      if (!t instanceof Map) ret pair(intRange(i, j-1), t); // leaf!

      tree = (Map) t;

    }

    if (best != null) ret pair(intRange(i, bestIndex), best);

    i += 2;

  }

  null;

}