proposition: Lemma fft1S n w p : fft1 n.+1 w p = let ev := fft1 n (w ^+ 2) (even_poly p) in let ov := fft1 n (w ^+ 2) (odd_poly p) in \sum_(j < 2 ^ n) ((ev`_j + ov`_ j * w ^+ j) *: 'X^j + (ev`_j - ov`_ j * w ^+ j) *: 'X^(j + 2 ^ n)).
proof: Proof. by []. Qed.
imports: mathcomp(all_ssreflect all_algebra ssrnum) digitn