-1. Add CartesianProductEJA.
+1. Add references and start citing them.
-2. Check the axioms in the constructor when check != False?
+2. Profile (and fix?) any remaining slow operations.
+
+3. When we take a Cartesian product involving a trivial algebra, we
+ could easily cache the identity and charpoly coefficients using
+ the nontrivial factor. On the other hand, it's nice that we can
+ test out some alternate code paths...
+
+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. Eliminate the matrix_space() override in CartesianProductEJA.