Lynness: recommendation

It took me a few minutes to figure out that William was Billy. My
sister Kate is an avid reader and checks our book blog occasionally- she
has a recommendation for him:

So, on the Hawkes book club Rae posted asking for scifi/fantasy
suggestions for William. Because I can't post on there I thought I'd
pass a suggestion along to you.

Anyway the post was about Douglas Adams' Hitchhiker's series and wanting
similar titles. The Xanth chronicles are pretty good but if you want the
British humor a really good series is Terry Pratchett's Discworld.