 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 Lemma34: :: Lemma to Theorem 3.4
  Tern (a,b`,b) = a
  proof
    Tern (a,b`,b) = Tern (Tern (a,b,b`), b`, b) by TRADef
      .= Tern (Tern (a,b,b`), b`, Tern (a,b,b)) by TRIDef
      .= Tern (a,b,Tern (b`,b`,b)) by TDis
      .= Tern (a,b,b`) by TLIDef
      .= a by TRADef;
    hence thesis;
  end;
