static IntRange find2_range(S pat, LS tok) {
  ret find2_range(parse3(pat), tok);
}

static IntRange find2_range(LS pat, LS tok) {
  for (int idx = 0; idx < tok.size(); idx += 2) {
    S[] result = find2(pat, tok, idx);
    if (result != null) ret intRange(idx, idx+l(pat)-2);
  }
  null;
}