proposition: Lemma b2mxK n (X : n.-tuple vT) i : r2v (row i (b2mx X)) = X`_i.
proof: Proof. by rewrite rowK v2rK -tnth_nth. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop finfun tuple) mathcomp(ssralg matrix mxalgebra zmodp)