reserve X for non empty TopSpace;
reserve X for non empty TopSpace;
reserve X for non empty TopSpace,
  X0 for non empty maximal_Kolmogorov_subspace of X;

theorem
  for a being Point of X, b being Point of X0 st a = b holds (
  Stone-retraction(X,X0))" Cl {b} = Cl {a}
by Def9,Lm2;
