more on the PP104 reading

I decided to add a sequencing exercise to the first reading; it may actually be too difficult, and in "the real world," I'd quickly discover whether that was the case by looking at student results.

When I was creating the sequencing exercise, I noticed that the readings needed to be modified slightly, so I made the modifications. This meant removing the previous html files and FTPing the updated ones, of course.

D. O.