theorem FINSEQ681:
  for f be FinSequence, a,b be Nat holds (f/^a)/^b = f/^(a+b)
  proof
    let f be FinSequence, a,b be Nat;
    ex D be non empty set st
     f is FinSequence of D by Th0;
    hence thesis by FINSEQ_6:81;
  end;
