reserve i,j,k,l for natural Number;
reserve A for set, a,b,x,x1,x2,x3 for object;
reserve D,D9,E for non empty set;
reserve d,d1,d2,d3 for Element of D;
reserve d9,d19,d29,d39 for Element of D9;
reserve p,q,r for FinSequence;

theorem
  for f being sequence of D holds f|(Seg i) is FinSequence of D
  proof
    reconsider i as Nat by TARSKI:1;
    for f being sequence of D holds f|(Seg i) is FinSequence of D by Th23;
    hence thesis;
  end;
