Sample questions from last two weeks of class

In these two weeks we spent most of our time on Gries and Persistent programming languages. 

1. Gries has questions in every chapter that are useful to try.  Here is a sampling that you should be able to do:
   1. Exercises for Chapter 10, Q1, Q3, Q4, Q5
   2. Exercises for Chapter 11,  Q8-12.  For some of these questions, you should pretend that the question does not give you the invariant and derive it yourself based on reading the code
   3. Exercises for Section 15.1, Q1, Q3
2. The abstract type mechanism described on page 18 gives a programming language syntax for existentially quantified types.  Do you think the language syntax in Atkinson and Morrison is stronger, weaker, or equally powerful to the existential types in lambda calculus? Give examples to support your argument.
3. For the existentially quantified type (absRealCounter) described on page 18 of Atkinson and Morrison, use the lambda calculus notation (using pack and unpack).