Section StructuralLinear.
Canonical diag_mx_additive n := Additive (@diag_mx_is_linear n).
Canonical diag_mx_linear n := Linear (@diag_mx_is_linear n).

Lemma row_diag_mx n (d : 'rV_n) i :
row i (diag_mx d) = d 0 i *: delta_mx 0 i.