From this point forward we may think of idempotents, selectives, and zero-one diagonal matrices as being roughly equivalent notions. The only reason I say roughly is that we are comparing ideas at different levels of abstraction in proposing those connections.
We have covered the way Peirce uses his invention of the comma modifier to assimilate boolean multiplication, logical conjunction, and what we may think of as serial selection under his more general account of relative multiplication.
But the comma functor has its application to relative terms of any arity, not just the arity of absolute terms, and so there will be a lot more to explore on this point. But now I must return to the anchorage of Peirce’s text and hopefully get a chance to revisit this topic later.