Section BlockMatrixRec.
Local Notation e := (mxsize_recl, mxsize_recl).
Local Notation l0 := (lift ord0).
Context {T : Type}.

Lemma mxrowEblock {q : nat} {q_ : 'I_q -> nat} m
(R_ : forall j, 'M[T]_(m, q_ j)) :
(\mxrow_j R_ j) =
castmx (big_ord1 _ (fun=> m), erefl) (\mxblock_(i < 1, j < q) R_ j).