theorem
  for q being FinSubsequence holds Seq q = Seq Shift(q,i)
proof
  let q be FinSubsequence;
A1: dom Seq q = dom Seq Shift(q,i) by Th55;
  for x being object holds
   x in dom Seq q implies (Seq Shift(q,i)).x = (Seq q).x by Th57;
  hence thesis by A1;
end;
