The Annotated Pratchett File, v7a

Dream Park: The Californian Voodoo Game, by Larry Niven and Stephen Barnes, 1991.

The UK edition of this book describes the character Alan Myers as “a Terry Pratchett wizard”. In the U.S. edition this sentence was simply left out.

At a later point in the novel (both editions this time), two characters exchange the following lines:

It’s been, what—five years?

Since the Diskworld Game. Ah... Hamburg.
Note the misspelling of Discworld.

Object-Oriented Languages, Systems and Applications, by Blair, Hutchinson, Gallagher and Shepherd, 1991.

“Consider the domain of Colours. If we have Red, Green and Blue, but now widen the domain to include Octaroon, an old program may read an unknown value from a new instance. Conversely, if we begin with Octaroon included, but now decide we no longer believe in Magic and remove it thus narrowing the domain, [...]”

Again, note the misspelling, this time of ‘Octarine’. Since this is a formal textbook, The Colour of Magic gets a proper mention in the references.