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

theorem
  for a,b,c being Function of Y,BOOLEAN holds (a '&' b) 'imp' c =
  a 'imp' ('not' b 'or' c)
proof
  let a,b,c be Function of Y,BOOLEAN;
    let x be Element of Y;
    (a 'imp' ('not' b 'or' c)).x =(a 'imp' (b 'imp' c)).x by BVFUNC_4:8;
    hence thesis by Th7;
end;
