reserve n for Nat,
  k for Integer;

theorem Th9:
  for p,q,r being FinSequence holds len (p ^ q) <= len (p ^ (q ^ r ))
proof
  let p,q,r be FinSequence;
  len (p ^ q ^ r) = len (p ^ (q ^ r)) by FINSEQ_1:32;
  hence thesis by CALCUL_1:6;
end;
