* @param arg
   * @param module
   * @param environment
   * @return boolean
   */
  public static boolean isTrueUnaryProposition(LogicObject relation, Stella_Object arg, Module module, Environment environment) {
    return (PLI.helpGetPropositions(relation, Cons.consList(Cons.cons(arg, Stella.NIL)), 1, module, environment) != null);
  }