Case sensitivity in 5.9.1



Hi,
regarding case sensitivity, can somebody please help me?:

My students are using Maxima 5.9.1 and I've copied into their disks
plotdf.lisp, from share/contrib/ in the CVS repository.

That file defines function "plotdf", but Maxima only recognizes PLOTDF:

Maxima restarted.
(%i1) load(plotdf);

(%o1)          /usr/share/maxima/5.9.1/share/contrib/plotdf.lisp
(%i2) plotdf([y,-x]);

(%o2)                          plotdf([y, - x])
(%i3) PLOTDF([y,-x]);

(%o3)                                  0

How can I make plotdf() work in Maxima 5.9.1?

Cheers,
Jaime