  Let A be a central division algebra over a field F with ind A = n. In
computing canonical p-dimension of projective PGL_1(A)-homogeneous varieties,
for p prime, we can reduce to the case of generalized Severi-Brauer varieties
X_e(A) with ind A a power of p divisible by e. We prove that canonical
2-dimension (and hence canonical dimension) equals dimension for all X_e(A)
with ind A = 2e a power of 2.
