reserve Y for non empty set,
  a,b,c,d for Function of Y,BOOLEAN;
reserve Y for non empty set,
  a,b,c for Function of Y,BOOLEAN;

theorem Th33:
  a 'nor' (b '&' c) = 'not' (a 'or' b) 'or' 'not' (a 'or' c)
proof
  a 'nor' (b '&' c) = 'not' (a 'or' (b '&' c)) by Th2
    .= 'not' ((a 'or' b) '&' (a 'or' c)) by BVFUNC_1:11;
  hence thesis by BVFUNC_1:14;
end;
