  Further results are reported for the one-component quaternionic wave equation
recently introduced. A Lagrangian is found for the momentum-space version of
the free equation; and another, nonlocal in time, is found for the complete
equation. Further study of multi-particle systems has us looking into the
mathematics of tensor products of Hilbert spaces. The principles of linearity
and superposition are also clarified to good effect in advancing the
quaternionic theory.
