proposition: Lemma det_lblock n1 n2 Aul (Adl : 'M[R]_(n2, n1)) Adr : \det (block_mx Aul 0 Adl Adr) = \det Aul * \det Adr.
proof: Proof. by rewrite -det_tr tr_block_mx trmx0 det_ublock !det_tr. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype finfun bigop finset fingroup perm order) mathcomp(div prime binomial ssralg countalg finalg zmodp)