theorem Th24:
  for k being Nat st len p < k & k <= len(p^q) holds (p^q).k = q.(k - len p)
proof
  let k be Nat;
  assume len p < k & k <= len(p^q);
  then len p + 1 <= k & k <= len p + len q by Th22,NAT_1:13;
  hence thesis by Th23;
end;
