theorem Th32: :: Theorem 3.2
  Tern (a,b,a) = a
  proof
    Tern (a,b,a) = Tern (Tern (a,b,b`),b,a) by TRADef
                .= Tern (Tern (a,b,b`),b,Tern (a,b,b`)) by TRADef
                .= Tern (a,b,Tern(b`,b,b`)) by TDis
                .= Tern (a,b,b`) by TLADef
                .= a by TRADef;
    hence thesis;
  end;
