Book 3.3.5: Function parameters are used inconsistently

[dimitry-ishenko]

In Chapter 3.5 we can't seem to settle on which letter to use as a parameter for the CDF and keep switching between $x$ and $r$. This is not a big deal, just a bit disorienting. Here is a sample:

This also occurs throughout other parts of the book, but just happened to catch my attention here.

[hollasch]

Moving into the v4.0.0 milestone for consideration. We may or may not punt this for the actual v4.0.0 release, depending on our progress.