SWI-Prolog Easter Egg - Hitchhiker's Guide to the Galaxy Referance

Simply type this at the prompt:

Trace.

(make sure you use a capital T)

And a referance for Hitchhiker's Guide to the Galaxy will appear.

Enjoy!

This is the result you should see:

?- Trace.
% ... 1,000,000 ............ 10,000,000 years later
%
% >> 42 << (last release gives the question)
?-