theorem
  f is FinSequence of D implies
    f|n is FinSequence of D & f/^n is FinSequence of D
  proof
    assume
    A1: f is FinSequence of D;
    (f|n)^(f/^n) = f by RFINSEQ:8;
    hence thesis by A1,FINSEQ_1:36;
  end;
