Section semiring.
Variables (S : {pred R}) (ringS : semiringPred S) (kS : keyed_pred ringS).
Fact mxOver_mul_subproof : mulr_closed (@mxOver n.+1 n.+1 _ kS).
End BlockRowRecL.

Lemma mxcol_recu {T : Type} {p : nat} {p_ : 'I_p.+1 -> nat} m
(B_ : forall j, 'M[T]_(p_ j, m)) :
\mxcol_j B_ j = castmx (mxsize_recl, erefl)
(col_mx (B_ 0) (\mxcol_j B_ (lift ord0 j))).