-4. Can we hit "x" with the deortho matrix and delegate to the
- _rational_algebra to speed up minimal_polynomial?
-
-5. In CartesianProductEJA we already know the multiplication table and
- inner product matrix. Refactor things until it's no longer
- necessary to duplicate that work.
-
-6. Figure out how to remove Unital() from subalgebras.
+4. Conjecture: if x = (x1,x2), then det(x) = det(x1)det(x2). This
+ should be used to fix the fact that det(x) is monstrously slow in
+ Cartesian product algebras, and thus randomly in the doctests.