New chapter coming soon.

I'm finally getting almost done with another chapter. I actually have almost as much material written that I haven't published yet as what's on the site, but it's in a lot of half-finished chapters. The next chapter was difficult because I wasn't sure whether I could go straight to the four-dimensional polytopes or whether more material on linear algebra was necessary. But finally I decided to focus on linear algebra, so the next chapter will be on the exterior algebra, eigenvalues, and polynomials. Then finally on to four dimensions!