theorem Th61:
  for k being natural Number holds k |-> d is FinSequence of D
proof
  let k be natural Number;
  set s = k |-> d;
  rng s c= {d} by FUNCOP_1:13;
  then rng s c= D by XBOOLE_1:1;
  hence thesis by FINSEQ_1:def 4;
end;
