Section Induction.
Definition matrix_rect := mx_ind.
Definition matrix_rec := mx_ind.
Definition matrix_ind := mx_ind.

Lemma mxsub_ind
(weight : forall m n, 'M[R]_(m, n) -> nat)
(sub : forall m n m' n', ('I_m' -> 'I_m) -> ('I_n' -> 'I_n) -> Prop)
(P : forall m n, 'M[R]_(m, n) -> Type) :
(forall m n (A : 'M[R]_(m, n)),
(forall m' n' f g, weight m' n' (mxsub f g A) < weight m n A ->
sub m n m' n' f g ->
P m' n' (mxsub f g A)) -> P m n A) ->
forall m n A, P m n A.