theorem Th4: (VAL g).TVERUM = 1
  proof
    thus (VAL g).TVERUM = (VAL g).TFALSUM => (VAL g).TFALSUM by LTLAXIO1:def 15
    .= FALSE => (VAL g).TFALSUM by LTLAXIO1:def 15
    .= 1;
  end;
