More semi-ring dictionaries, and Chapter 13 of SOFP

Let's pick up our discussion from around Section 3.3 of Functional Collection Programming with Semi-ring Dictionaries (https://arxiv.org/abs/2103.06376), and then if time permits, resume Chapter 13 of The Science of Functional Programming (https://www.dropbox.com/scl/fi/v6st93ahgp44pehqeyl1i/sofp-draft-2023-09-30.pdf?rlkey=3cplruvoer9ecns9ne66hpzfw&dl=0), where I believe we stopped around Section 13.2.

We'll post the link to the meeting on this page shortly before the scheduled start of the meeting.