// returns remaining conditions
static Exp nlLogic_checkFirstConditions(NLLogicChecker_v2 c, IfThen rule, NLLogicChecker_v2.Matching m) {
  Exp exp = rule.in;
  while ping (exp != null) {
    Pair<Bool, Exp> p = c.checkFirstCondition(exp, m);
    if (!p.a) break;
    exp = p.b;
  }
  ret exp;
}