History: Started based on the SICP symbolic differentiation chapter, with some extensions. Brought into Incanter, additions made by David Edgar Liebke. Now, split back into its own project to support a more rapid development cycle, the addition of unit tests & generative testing, expression simplification, etc. Please don't actually use this until the tests pass. Licensed under the EPL, see "epl-v10.html" Copyright 2012 Bryce Nyeggen and David Edgar Liebke