Maxima style



Dear Maxima-team & users,

I have made simple image using Maxima
http://commons.wikimedia.org/wiki/File:Dynamic_internal_and_external_rays_.svg

The source code is included.

Code works , but I would like to ask :
if the code is in proper Maxima style ?
Can I do it better ?

I remember that :
it is better to use define instead of :=


Sth more ?


TIA

Adam