rules for non-commutative-multiplication



Hallo all,
I ran into problems when setting rules for the non-commutative 
multiplication operator .
It seems that rules don't take advantage of associativity.
I tried to implement three-dimensional geometric algebra with the
following commands (comment: Of course I now that one should use 
matchdeclare to avoid repetion of similair lines, but I want to make the 
rules to be easily understandable by students):

tellsimpafter(e[1].e[1],1)$
tellsimpafter(e[2].e[2],1)$
tellsimpafter(e[3].e[3],1)$
tellsimpafter(e[2].e[1],-e[1].e[2])$ tellsimpafter(e[3].e[2],-e[2].e[3])$
tellsimpafter(e[3].e[1],-e[1].e[3])$

With this, e[2].e[1] simplifies as expected to -e[1].e[2] but
e[2].e[1].e[3] does not. How can one trick tellsimpafter into taking
advantage of associativity?
Any hints?
Reinhard