The dir1 example was modified multiple times in this chapter.  
Here:

- dir1_start is its initial state in the opening demo
- dir1_finish is its final state in the opening demo
- dir1_rel is its state at the end of the relative-imports demo

To use these folders to test, first copy one of them to name 
"dir1".  The imports coded within them assume that name.

Also here, ns is the final state of the namespace-package demo, and
system1 shows what the hypothetical example of the same name would
look like if coded to support both program and package modes.