proposition: Lemma rank_normal u : (\rank (u ^_|_) >= n.-1)%N.
proof: Proof. rewrite mxrank_ker -subn1 leq_sub2l //. by rewrite (leq_trans (mxrankM_maxr _ _)) // rank_leq_col. Qed.
imports: HB(structures) mathcomp(all_ssreflect ssralg fingroup zmodp poly ssrnum) mathcomp(matrix mxalgebra vector falgebra ssrnum algC algnum) mathcomp(fieldext) mathcomp(vector)