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

theorem
  for a being Function of Y,BOOLEAN holds I_el(Y) 'imp' a = a
proof
  let a be Function of Y,BOOLEAN;
    let x be Element of Y;
    (I_el(Y) 'imp' a).x ='not' (I_el(Y)).x 'or' a.x by BVFUNC_1:def 8
      .=FALSE 'or' a.x by BVFUNC_1:def 11;
    hence thesis;
end;
