I received an overwhelming response to the introductory blog post about the algebra of graphs; thank you all for your remarks, questions and suggestions! In the second part of the series I will show that the algebra is not restricted only to directed graphs, but can be extended to axiomatically represent undirected graphs, reachability and dependency graphs (i.e. preorders and partial orders), their various combinations, and even hypergraphs.

**Update:** This series of blog posts was published as a functional pearl at the Haskell Symposium 2017.