proposition: Lemma row'_col'_char_poly_mx m i (M : 'M[R]_m) : row' i (col' i (char_poly_mx M)) = char_poly_mx (row' i (col' i M)).
proof: Proof. apply/matrixP=> k l; rewrite !mxE. suff ->: (lift i k == lift i l) = (k == l) => //. by apply/inj_eq/lift_inj. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq path) mathcomp(ssralg fintype finfun perm matrix bigop zmodp mxalgebra) mathcomp(choice poly polydiv mxpoly binomial)