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 Th1:
  rng XSeq c= Si
proof
  let x be object;
  assume x in rng XSeq;
  then ex n being Nat st x = XSeq.n by SETLIM_1:4;
  hence thesis;
end;
