proposition: Lemma v2rK : cancel v2r r2v.
proof: Proof. by have/bij_can_sym:= r2vK; apply. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop finfun tuple) mathcomp(ssralg matrix mxalgebra zmodp)