 reserve T for Ternary_Boolean_Algebra;
 reserve a,b,c,d,e for Element of T;
 reserve x,y,z for Element of T;

theorem Lemma0: :: Theorem 3.4
  a`` = a
  proof
    a = Tern(a``, a`, a) by TLADef
     .= a`` by Lemma34;
    hence thesis;
  end;
