Hi Peter, author here. Thanks for weighing in with the extra context on index skip scan, and huge thanks for adding this to Postgres.

I’m going to revise the multi-column index section to be more precise about when leftmost-prefix rules apply, and I’ll include a note on how skip scan changes the picture

Oh, this is fun! I love the idea of simple games like this and stranger.video!

This series of challenges from Fly.io seems to be good: https://fly.io/dist-sys/