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).

Lemma eq_mxblockP A_ B_ :
(forall i j, A_ i j = B_ i j) <->
(\mxblock_(i, j) A_ i j = \mxblock_(i, j) B_ i j).