proposition: Lemma inj2_proj2 : inj2 ** proj2 = idm.
proof: Proof. by apply: val_inj; rewrite /= mul_row_col mulmx0 mul1mx add0r. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq path) mathcomp(ssralg fintype perm choice matrix bigop zmodp mxalgebra poly) ssrcomplements stronglydiscrete coherent edr