Working on the chapters on counterfactual conditionals for the Open Logic Project, I needed some illustrations for David Lewis's sphere models, which he jokingly called "Ptolemaic astronomy." Since Franz Berto joked that this should just require \usepackage{ptolemaicastronomy}, I wrote some LaTeX macros to make this easier using TikZ. You can download ptolemaicastronomy.sty (it should work … Continue reading Ptolemaic Astronomy
![](https://i0.wp.com/richardzach.org/wp-content/uploads/2018/03/spheremodel.png?fit=622%2C570&ssl=1)