theorem Th2: NAT --> {} is LTLModel
  proof
    set M = NAT --> {};
A1: now
      let x be object;
      assume x in NAT;
      then A2: M.x = {} by FUNCOP_1:7;
      {} c= props;
      hence M.x in bool props by A2;
    end;
    dom M = NAT by FUNCOP_1:13;
    hence thesis by A1,FUNCT_2:3;
  end;
