(* (Integral) Cyclotomic polynomials. *)
Notation "''Phi_' n" := (Cyclotomic n)
(at level 8, n at level 2, format "''Phi_' n").

Lemma prod_Cyclotomic n :
(n > 0)%N -> \prod_(d <- divisors n) 'Phi_d = 'X^n - 1.