Homework 3:

   - read CPDT 3.1-3.5

   - Investigate what happens if we define a type that is like numbers but
     with no base case: 

       Inductive weird : Set :=
          | W : weird -> weird.

Try to predict the induction principle for this type (then use Coq to check
your answer), and explain what it means.  Then prove (in Coq) that this type
is uninhabited.

This is a pretty easy assignment because the interesting part of chapter 3
is what we'll come to on Monday!  If you feel you want some more exercises
because you haven't seen this stuff so much, I can suggest some good
exercises from the Software Foundations material -- just let me know.