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 Th50:
  dom Complement F1 = dom F1
proof
  thus dom Complement F1 = Seg len Complement F1 by FINSEQ_1:def 3
    .= Seg len F1 by Def5
    .= dom F1 by FINSEQ_1:def 3;
end;
