Book excerpt: Thank heavens for Jens Wittenburg, of the University of Karlsruhe in Germany. Anyone who’s been laboring for years over equation after equation will want to give him a great big hug. It is common practice to develop equations for each system separately and to consider the labor necessary for deriving all of these as inevitable. Not so, says the author. Here, he takes it upon himself to describe in detail a formalism which substantially simplifies these tasks.