// return new statement or null if it existed
static LispStatement lispAddLocalTruth(Lisp l) {
  if (lispTrue(l)) null;
  ret lispAddLocalTruth_noCheck(aGlobalID(), l);
}

static LispStatement lispAddLocalTruth(S id, Lisp l) {
  if (lispTrue(l)) null;
  ret lispAddLocalTruth_noCheck(id, l);
}

static LispStatement lispAddLocalTruth_noCheck(S id, Lisp l) {
  LispStatement s = new LispStatement(id, l);
  lispStatements_cached().put(id, s);
  lispChange();
  ret s;
}