ewrite -in_factmodJ // -mulmxA -repr_mxM.
Qed.

(* Specifications: *)
Qed.
Qed.
Arguments cyclic_mxP {u v}.
Qed.
(\bigcap_j kermx (vec_mx (row j (annihilator_mx u))))%MS.
Qed.
Proof. exact: eqmx_iso. Qed.
Qed.
Proof. by case=> f injf _ <-; rewrite mxrankMfree ?row_free_unit.
Qed.
Qed.
[&& mxmodule V, (V :&: row_hom_mx (nz_row U))%MS != 0 & \rank V <= \rank U].
Qed.