Not me, the authors -- I'm a fly on the wall compared to them ;) This is some serious work, I just did a fast implementation. Re implementation -- it turns out that there are parts of some standard libraries that this problem pushes to its limits, that we had to go around during implementation. So there were still some cool challenges involved. I was also pretty happy about the late binding/lazy evaluation thing I came up with. Of course Knuth just did it (check his notes), without even thinking about it :D What is an achievement for me is a lazy Monday coffee for him, but oh well!