# Resource for Problem 5

I stumbled across a paper by Gian-Carlo Rota last night that deals with incidence algebras.  I haven’t finished reading it yet, but it looks like it has some insight into what’s going on here.  If anyone wants to take a look at it, here’s the link.

dedekind.mit.edu/~rstan/pubs/pubfiles/10.pdf

A nice resource on this and many, many more topics having to do with posets and lattices, is the textbook $textit{Combinatorics: The Rota Way}$.