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 Th39:
  for A being Event of Sigma holds P.A = (COM P).A
proof
  reconsider C = {} as thin of P by Th24;
  let A be Event of Sigma;
  thus P.A = (COM P).(A \/ C) by Def8
    .= (COM P).A;
end;
