 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 Th35: :: (2.36)
  ((-(a => b)) => (a "/\" -b)) "/\" ((a "/\" -b) => -(a => b)) = Top L
  proof
A1: -(a => b) < (a "/\" -b) by Def10;
    (a "/\" -b) < -(a => b) by Def9;
    hence thesis by A1;
  end;
