Interesting, by looking up mapcan, I came across the Simplified Lisp Reference:

http://jtra.cz/stuff/lisp/sclr/mapcan.html

Also linked from the resources-section of:

http://gettingstartedwithcommonlisp.com/

I don't think I've come across the simplified reference before -- appears to be a good resource for those of us starting out with lisp -- striking a balance between all of CLOS and the sometimes simplistic presentation of text books.