
theorem Th1:
  for D be set for p be FinSequence for n be Nat holds p
  in D* implies p|Seg n in D*
proof
  let D be set;
  let p be FinSequence;
  let n be Nat;
  assume p in D*;
  then p is FinSequence of D by FINSEQ_1:def 11;
  then p|Seg n is FinSequence of D by FINSEQ_1:18;
  hence thesis by FINSEQ_1:def 11;
end;
