reserve X for set;

theorem
  for S being SigmaField of X, M being sigma_Measure of S, T being
N_Sub_set_fam of X st (for A being set st A in T holds A in S) holds union T in
  S & meet T in S
proof
  let S be SigmaField of X, M be sigma_Measure of S, T be N_Sub_set_fam of X;
  assume
A1: for A being set st A in T holds A in S;
  T c= S
  by A1;
  hence thesis by Def5,Th22;
end;
