First of all: last week, the Deranged Mathematician hit 1k subscribers. Thank you very much to all of you who made that possible!

Now, for the meat of this post: I have turned on paid subscriptions for the blog. Everything that was free before still is, and I only intend to keep about 50% of all posts behind a paywall. If you want the full details and/or to participate in a poll about what will be the first longer lecture series, see here: Updates to the Deranged Mathematician

Aside from providing access to the full archive, paid subscriptions also grant access to the draft of my book, A Projective Perspective on Linear Fractional Transformations . In some sense, this is a more "grown-up" version of my existing book, Linear Fractional Transformations: An Illustrated Introduction , published by Springer. The new book is aimed at an upper-level undergraduate audience and covers inversive, Minkowski, and hyperbolic geometry.…