Note:
Submission is optional but recommended; try your best.
We'll discuss some of these on Tuesday 12/17's review session.

subtyping (chap. 15):

1. 15.5.2 (S-Ref)

2. 15.5.3 (S-Array)

3. give an example term that is well-typed using only Source
   (but untypable using S-Ref), and an example typable with Sink
   (but untypable using S-Ref).

4. under the new variant definition, consider term:
   	 
	 case <l2=5> of <l1=x1>=>x1
	      	     	<l2=x2>=>ref x2
 
   draw the typing derivation.   


featherweight java (chap. 19):

0. evaluate term
   	    new Pair(new A(), new B()).setfst(new B())
   all the way to a value.
   also show its typing derivation.

1. give an example of overriding and downcasting.
   why is downcasting unavoidable?

2. reformulate preservation theorem w/o the stupid casting rule.

3. define big-step semantics for FJ evaluation.

4. 19.4.5. Note: you don't need to know what is algorithmic subtyping.
   All you need to notice is that \gamma |- t : T means different things
   in chap. 15 and chap. 19. What is that crucial difference?

5. What can you say b/w evaluation context and congruence rules?
   Do you have a better understanding of congruence rules now?

6. What's your understanding of the override rule?