theorem
  for X0 being non empty SubSpace of X, x being Point of X st x in the
  carrier of X0 holds (incl X0).x = x
proof
  let X0 be non empty SubSpace of X, x be Point of X;
  assume x in the carrier of X0;
  hence (incl X0).x = (id X).x by FUNCT_1:49
    .= x;
end;
