reserve Y for non empty set;
reserve Y for non empty set;
reserve Y for non empty set;

theorem
  for a,b being Function of Y,BOOLEAN holds a = (a '&' b) 'or' (a
  '&' 'not' b)
proof
  let a,b be Function of Y,BOOLEAN;
    let x be Element of Y;
    ((a '&' b) 'or' (a '&' 'not' b)).x =(a '&' (b 'or' 'not' b)).x by
BVFUNC_1:12
      .=(a '&' I_el(Y)).x by BVFUNC_4:6
      .=a.x by BVFUNC_1:6;
    hence thesis;
end;
