Here’s a quick way to add an item to a sorted list:
(merge 'list (list item) sorted-list test)
Via Bernhard Pfahringer on comp.lang.lisp, 1998.
Among the 4 Lisp’s equality operators equalp may be the least used, but it has some really cool features:
The last 3 are really useful, because unlike strings and other primitive types, there’s no specialized equality predicates for built-in structural types, so equalp fills this role.
(contributed by @vseloved)