theorem Th5: not A is conditional implies tau1.A = {A}
  proof
    assume not A is conditional;
    then A is conjunctive or A is simple or A = TFALSUM by HILBERT2:9;
    then ex r, s st A = r 'U' s or ex n st A = prop n or A = TFALSUM
    by HILBERT2:def 8,HILBERT2:def 6;
    hence thesis by Def4;
  end;
