static Pair<Collection<Attractor>, Set<S>> applyAttractors_getRuleAndStringEmits(L<? extends Attractor> rules, S s) {
  new L<Attractor> newRules;
  Set<S> strings = ciSet();
  
  for unnull (Attractor rule : rules)
    if (rule.matches(s)) {
      L emits = getEmits(rule);
      addAll(newRules, instancesOf Attractor(emits));
      addAll(strings, stringsOnly(emits));
    }
    
  ret pair(newRules, strings);
}