  I present an alternative and rather direct way to derive the well known
Schr\"odinger equation for a quantum wavefunction, by starting with the Klein
Gordon equation and applying a directional factorization scheme. And since if
you have a directionally factorizing hammer, everything looks like a
factorizable nail, I also derive an alternative wavefunction propagation
equation in the momentum-dominated limit. This new Schr\"odinger $p$-equation
therefore provides a potentially useful complement to the traditional
Schr\"odinger $m$-equation's mass-dominated limit.
