theorem Th23:
  for f being Function of Seg i, D holds f is FinSequence of D
proof
  let f be Function of Seg i, D;
  reconsider i as Element of NAT by ORDINAL1:def 12;
  dom f = Seg i by FUNCT_2:def 1;
  then
A1: f is FinSequence by FINSEQ_1:def 2;
  rng f c= D by RELAT_1:def 19;
  hence thesis by A1,FINSEQ_1:def 4;
end;
