Correction to my suggestion id+di = 0. Don't do it. id = di is fine as it stands for refined complex numbers, which should be represented in C(2) = 2x2 complex matrices (embeddable in R(4) - 4x4 real matrices) as the obvious extension of the refined reals x+yd. I shouldn't have been so smug about 4D Clifford algebras, this algebra of refined complex numbers doesn't satisfy d^4 = 1, needed if d is to be a Clifford generator. And in fact although di = 1 0 0 0 we have id = 0 0 0 1 (I should have checked that more carefully.) I thought about trying to make the infinitesimals points on the "light cone" of R(2) (the singular matrices) but couldn't get that to work. So 2x2 complex matrices with id = di is the best I could think of. This works for modeling the refined complex numbers (barring any other errors), but with nothing left to motivate id+di = 0. The representation x+iy+dv+idw is fine, with idw = diw = wid etc., all is commutative. (I was hoping too hard for the excitement of noncommutativity, this is boringly noninteractive as it stands.) Vaughan