theorem Th22: p => TVERUM is ctaut
  proof
    let g;
    set v = VAL g;
A1: v.p = 1 or v.p = 0 by XBOOLEAN:def 3;
    thus v.(p => TVERUM) = v.p => v.TVERUM by LTLAXIO1:def 15
    .= 1 by A1,Th4;
  end;
