static <A, B> A reverseLookup(B value, Map<A, B> map) {
  ret reverseLookup(map, value);
}

static <A, B> A reverseLookup(Map<A, B> map, B value) {
  if (map != null && value != null) for (A key : map.keySet())
    if (eq(map.get(key), value))
      ret key;
  ret null;
}