deeply embedded branches: complex structure created by repeated
application of simple rules.
-The best way to follow the next long, somewhat intricate paragraph
-immediately following is to take this type and try to construct a term
-for it, just as we did for the monads above. If you suceed, the
-discussion will just make brilliant sense. If you get stuck, the
-discussion will explain how to proceed.
+[This would be a good time to try to build your own term for the types
+just given. Doing so (or attempting to do so) will make the next
+paragraph much easier to follow.]
As usual, we need to unpack the `u` box. Examine the type of `u`.
This time, `u` will only deliver up its contents if we give `u` an