static ItIt<Matches> flexMatchIC_tok_iterator(Tok pat, Tok input) {
  LS tokPat = pat.tok(), tokInput = input.tok();
  L<Int> varIndices = flexMatchIC_getVarIndices(tokPat, tokInput);
  if (varIndices == null) ret emptyItIt();

  ItIt<LS> spreadInputs = ai_spreadCertainIndices_2_iterator(pat.tok(), input.tok(), varIndices);
  
  ret mapI_notNulls(tok -> getMatches(tokPat, tokInput), spreadInputs);
}