theorem
  for X0 being non empty SubSpace of X, f being Function of X,Y holds f|
  X0 = f*(incl X0)
proof
  let X0 be non empty SubSpace of X, f be Function of X,Y;
  thus f|X0 = (f*(id X))|X0 by FUNCT_2:17
    .= f*(incl X0) by Th62;
end;
