
theorem
  for x,y being Element of BOOLEAN holds nor2.<*x,y*> = 'not' (x 'or' y)
& nor2a.<*x,y*> = 'not' ('not' x 'or' y) & and2.<*x,y*> = 'not' ('not' x 'or'
  'not' y) by Def5,Def6,Lm4;
