Force a variable to commute over the non-commutative operator dot

Hi,

I started using Maxima this morning and I would really appreciate it if
someone could help me out with the question I describe below. For the time
being it is even hard for me to choose the right keywords to google my
question, so please bear with me if my question is already answered
somewhere else or if it is too trivial.

Here we go:

I need to do some calculations that involve non-commutative multiplication -
nothing fancy, just tedious - but I need to have a variable that commutes
over the operator "."

For example I want to multiply

(t*(x-y)).(t*(x+y))

and get a t^2 factor in front. How do I get this?

Thanks a lot,

Pantelis