static ItIt<S> applyArbitraryVarsRule_flexFind_iterator(Set<S> vars, S ruleIn, S ruleOut, S input) {
  ret mapI(arbitraryVarsFlexFindIC_iterator_withPreAndPost(vars, ruleIn, input), map ->
    map.get("$_pre") + replaceVars_optRound2(ruleOut, map) + map.get("$_post"));
}