Add comment.
Add next section exercises.
Complete 2.4.
Start 2.5.
Centralize #pow and it's dependencies.

We'll need #pow to solve the next exercise.
Complete 2.5.
Complete 2.6.

I'm officially blown away.
Comment on #adder procedure.
Verify additive properties of #adder.
Add next section exercises.
Run all source files or just one.
Make it easier to run individual files.
Use less parenthesis in 2.6 assertions.
Use (let...) to clarify #adder.
Prepare for 2.1.4 section exercises.
Complete 2.7.
Complete 2.8.
Clean up.
2.9.
2.10