Slightly off topic: The title hits home. When I was young, books were a luxury item. Less rich people just used the library. But the library had a strict 7 books rental policy. Not enough for the avid reader that also needed a small programming reference library. So I had 3 steady, occasionally 4th, library card pool from family members to keep my bookshelf operational.
I also remember libraries having a very small limit back in the day, so I was surprised to find out that in the Bay Area libraries typically allow up to 100 books per card!
Mind blown. How can that work? I assume book rentals follow the usual Poisson distribution?