theorem Th46:
  for k being natural Number holds id Seg k is FinSequence of NAT
proof
  let k be natural Number;
  set I = id Seg k;
  reconsider k as Element of NAT by ORDINAL1:def 12;
  dom I = Seg k;
  then rng I = Seg k & I is FinSequence by FINSEQ_1:def 2;
  hence thesis by FINSEQ_1:def 4;
end;
