reserve n,m,k,i for Nat,
  g,s,t,p for Real,
  x,y,z for object, X,Y,Z for set,
  A1 for SetSequence of X,
  F1 for FinSequence of bool X,
  RFin for real-valued FinSequence,
  Si for SigmaField of X,
  XSeq,YSeq for SetSequence of Si,
  Omega for non empty set,
  Sigma for SigmaField of Omega,
  ASeq,BSeq for SetSequence of Sigma,
  P for Probability of Sigma;

theorem Th2:
  for f being FinSequence holds n in dom f iff n<>0 & n <= len f
proof
  let f be FinSequence;
  n in dom f iff n>=1 & n <= len f by FINSEQ_3:25;
  hence thesis by NAT_1:14;
end;
