move=> A; rewrite inE /= /invmx -if_neg => ->. Qed.

End Defs.Local Notation n := n'.+1.

Canonical matrix_algType :=

(* Specifications: *)
Lemma diag_mxC n (d e : 'rV[R]_n) :
Lemma mxtrace_mulC m n (A : 'M[
Qed.
Qed.
Qed.
Qed.
Qed.