Today I'll give you the hw2 handout, which has both a written and
a program part, due on Tuesday 2/21.

In particular we will introduce the hw2 program part.  This is not a
bluej project, but rather just a set of Java sources, of which you
edit just one file (PRedBlackBST.java).  Last time we looked at
PBST.java.  This time there are a few more details, in particular an
iterator (I added that since Wednesday).

You will be implementing insertion in a persistent left-leaning
red-black tree.  For extra credit, you may also try to implement a
more efficient (stack based) iterator.

See the files in:  ../hw2/