proposition: Lemma log2_pred_pow n: log2 ((2^ n).-1) = n.
proof: Proof. case: n => //n; apply: log2_pr. by rewrite -ltnS prednK ?expn_gt0 // leqnn andbT ltn_exp2l. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq choice fintype order bigop ssralg) mathcomp(div ssrnum ssrint rat prime path binomial) mathcomp(tuple finset) gaia(fibm)