Commutation with derivatives



Hi all! I need to define a function named Tr(x) which is linear and I 
want it to commute with derivative. For example, if I write 
diff(Tr(f(x)),x) I want maxima to perform Tr(diff(f(x),x)). This must be 
done without using an explicit defintion of the Tr function, but leaving 
it symbolic. I tried to give the command assume(Tr,linear), but it 
doesn't work fine.

Anyone knows how to solve this problem?

Thanks.
-- 

Gianluca Malato