@Cormullion:
From then "Introduction to newLISP" i think the difference function should be intersect in this example?
The intersect function finds the elements that are in both lists.
(difference d2 d1)
;-> ("." ".." ".DS_Store" "Language Modules" "Menu Scripts" "Plug-Ins" "Read Me.txt" "Scripts" "Unix Support")
You're quite right! Thanks for catching this one... It'll be fixed - one day. :)