+Our @code{compare-and-swap} is user-extensible using a protocol
+similar to @code{setf}, allowing users to add CAS support to new
+places via e.g. @code{defcas}.
+
+At the same time, new atomic operations can be built on top of CAS
+using @code{get-cas-expansion}. See @code{atomic-update},
+@code{atomic-push}, and €@code{atomic-pop} for example of how to do
+this.