> after noticing that Bruno Haible had posted an updated version of
> clisp, I compiled and installed it.
> Then I recompiled Maxima.
> ...
> After several hour's work with Maxima, I suddenly noticed that the
> differential operator diff(y, x) returns unevaluated.
Known bug. Try CVS maxima or a recent snapshot.
This works for me with clisp-2.33 on cygwin.