reserve n,m,k for Element of NAT,
  x,X for set,
  A1 for SetSequence of X,
  Si for SigmaField of X,
  XSeq for SetSequence of Si;
reserve Omega for non empty set,
  Sigma for SigmaField of Omega,
  ASeq for SetSequence of Sigma,
  P for Probability of Sigma;

theorem Th6:
  for A,B being Event of Sigma st A c= B & P.B = 0 holds P.A = 0
proof
  let A,B be Event of Sigma;
  assume A c= B & P.B = 0;
  then P.A <= 0 by PROB_1:34;
  hence thesis by PROB_1:def 8;
end;
