
theorem Th18:
  for X being set holds BoolePoset X, (BoolePoset{0})|^X are_isomorphic
proof
  let X be set;
  consider f being Function of BoolePoset X, (BoolePoset{0})|^X such that
A1: f is isomorphic and
  for Y being Subset of X holds f.Y = chi(Y,X) by Th17;
  take f;
  thus thesis by A1;
end;
