theorem for f be FinSequence of COMPLEX holds
  k in dom (f|n) implies k in dom f
  proof
    let f be FinSequence of COMPLEX;
    assume k in dom (f|n); then
    k in dom ((f|n)^(f/^n)) by FINSEQ_2:15;
    hence thesis by RFINSEQ:8;
  end;
