sbool ai_deriveOutput_debug;

static Set<S> ai_deriveOutput(L<IfThen> rules, LS facts) {
  final new NLLogicChecker_v3 c;
  c.facts = facts;
  c.rules = rules;
  final new NLLogicChecker_v2.Matching m;
  final new LinkedHashSet<S> out;
  for (final IfThen rule : nlLogic_filterByRHSConstructs(rules, 'output)) {
    if (ai_deriveOutput_debug)
      print("ai_deriveOutput: Checking " + rule);
    c.iterate(rule.in, m, r {
      if (ai_deriveOutput_debug)
        print("Got matches: " + sfu(m.matches));
        
      for (Exp e : nlLogic_unrollAnd(rule.out)) {
        if (e cast Func)
          if (eq(e.name, "output"))
            continue with out.add(nlLogic_text(c.apply(e.arg, m)));
        if (c.checkHelper(e, m))
          continue;
        print("Ignoring unknown RHS element: " + e);
      }
    });
  }
  ret out;
}

Began life as a copy of #1018057