+5. Compute the scalar in the general natural_inner_product() for
+ matrices, so no overrides are necessary.
+
+6. The main EJA element constructor is happy to convert between
+ e.g. HadamardEJA(3) and JordanSpinEJA(3).
+
+8. Add back the check_field=False and check_axioms=False parameters
+ for the EJAs we've constructed ourselves.