static int find2_index(S pat, LS tok) {
  ret find2_index(parse3(pat), tok);
}

static int find2_index(LS pat, LS tok) {
  for (int idx = 0; idx < tok.size(); idx += 2) {
    S[] result = find2(pat, tok, idx);
    if (result != null) ret idx+1;
  }
  ret -1;
}