1 + 1 = 2

Over at The Universe of Discourse, Mark Dominus has a nice article on Whitehead and Russell's Principia Mathematica from the viewpoint of a modern computer programmer.  One quotation:

... The notation is somewhat obscure, because mathematical notation has evolved substantially since then. And many of the simple techniques that we now take for granted are absent. Like a poorly-written computer program, a lot of Principia Mathematica's bulk is repeated code, separate sections that say essentially the same things, because the authors haven't yet learned the techniques that would allow the sections to be combined into one.