Variable n' : nat.
Local Notation n := n'.+1.
Canonical matrix_algType :=
Eval hnf in AlgType R 'M[R]_n (fun k => scalemxAr k).
End MatrixAlgType.

Lemma cofactor_tr n (A : 'M[R]_n) i j : cofactor A^T i j = cofactor A j i.