// vars can be a "degenerate set" (e.g. made with predicateToSet)
static ItIt<SS> arbitraryVarsFlexFindIC_iterator(Set<S> vars, S pat, S input) {
  new LS usedVars;
  S starsPat = arbitraryVarsToStars(pat, vars, usedVars);
  ret mapI(flexFindIC_iterator(starsPat, input), m -> matchesToMapUsingVarList_ciMap(m, usedVars));
}