The Houston Problem Book (wiki)

Reduction of the Black-Scholes equation to the Heat Equation

Solutions to "Special Functions" by Rainville

"Lemma vs. Theorem"

"How does a branch cut define a branch?"

Infinitesimal time scale calculus

2010 1 December - Construction of a regular 17-gon

Differential analyzer TiKz schematic: [pdf] [tex]

Five problems on a $2$-integrator differential analyzer and the sign of direction

The train running problem