I've been reading Alex Petrov's Database Internals to learn more about how databases are implemented. One of the topics covered in the book is a data structure known as the B-tree. Relational databases like Postgres, MySQL, and sqlite use B-trees as the data structure for storing the data on disk.
I was reading along with the book as Petrov explained how B-trees work, and nodding my head. But there's a difference between feeling like you understand something (what the philosopher C. Thi Nguyen calls clarity) and actually understanding it. So I decided to model B-trees using TLA+ as an exercise in understanding it better.
TLA+ is traditionally used for modeling concurrent systems: Leslie Lamport originally developed it to help him reason about the correctness of concurrent algorithms. However, TLA+ works just fine for sequential algorithms as well, and I'm going to use it here to model sequential operations on B-trees.