 reserve L for Quasi-Boolean_Algebra,
         x, y, z for Element of L;
 reserve L for Nelson_Algebra,
         a, b, c, d, x, y, z for Element of L;

theorem Th26: :: (2.27)
  (a => (a "\/" b)) = Top L
  proof
    a < a "\/" b by Th7;
    hence thesis;
  end;
