reserve X for set;

theorem
  for S being SigmaField of X, M being sigma_Measure of S holds {} in S
& X in S & for A,B being set st A in S & B in S holds X \ A in S & A \/ B in S
  & A /\ B in S by Def1,FINSUB_1:def 1,def 2,PROB_1:4,5;
