theorem Th6:
  for A being Subset-Family of Omega st A is intersection_stable &
  A c= Indep(B,P) holds sigma(A) c= Indep(B,P)
proof
  reconsider Indp = Indep(B,P) as Dynkin_System of Omega by Th5;
  let A be Subset-Family of Omega;
  assume A is intersection_stable & A c= Indep(B,P);
  then sigma(A) c= Indp by DYNKIN:24;
  hence thesis;
end;
