Birthday

Happy birthday, rfmcdpei!

DG, Part 0: Are We Not Geometers?

Before I begin with differential geometry proper, I'd like to make a few comments on the use of coordinates. Coordinate geometry was developed independently and more-or-less simultaneously by René Descartes and Pierre de Fermat in the 17th century, but they developed it for different purposes, and that difference has consequences that are worth glancing at.

( Coordinate *This*! )