Section BlockColRing.
Context {R : ringType} {n : nat} {p_ : 'I_n -> nat}.
Notation sp := (\sum_i p_ i)%N.
Implicit Type (s : 'I_sp).

Lemma submxblockD (B B' : 'M[V]_(sp, sq)) i j :
submxblock (B + B') i j = submxblock B i j + submxblock B' i j.