f.
by move=> isoUV simU; apply: mx_iso_simple (simU); apply/mxsimple_isoP.
Qed.

(* For us, "semisimple" means "sum of simple modules"; this is classically,   *)
(* but not intuitionistically, equivalent to the "completely reducible"       *)
(* alternate characterizat

(* Specifications: *)
Qed.
Qed.
Qed.
Qed.