reserve A,B,p,q,r,s for Element of LTLB_WFF,
  n for Element of NAT,
  X for Subset of LTLB_WFF,
  g for Function of LTLB_WFF,BOOLEAN,
  x,y for set;

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;
