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

Lemma mxcolEblock {p : nat} {p_ : 'I_p -> nat} n
(C_ : forall i, 'M[T]_(p_ i, n)) :
(\mxcol_i C_ i) =
castmx (erefl, big_ord1 _ (fun=> n)) (\mxblock_(i < p, j < 1) C_ i).