One of the ways that Emacs Lisp differs from other Lisps is that it doesn’t support multiple arguments for comparisons. That is, you can’t write things like
(if (= a b c) do-this else-do-that)
or
(when (< a b c) ...)
You can still express those comparisons, of course, but you have to connect two or more two-argument comparisons with and.
Now, as Bozhidar Batsov points out, that’s about to change. Emacs 24.4 will support variadic comparisons. That’s not a huge change but it does bring Elisp in line with other Lisps and makes it easier to express complex comparisons concisely and clearly. As I wrote before, I’m really impressed with this release and looking forward to its availability.