To simplify hw 1, part A and B:

In your UML class diagrams include only the classes 
that are mentioned in the files of the form *.cd:

http://www.ccs.neu.edu/home/lieber/com1205/f02/hw/1/binary-tree/tree.cd

http://www.ccs.neu.edu/home/lieber/com1205/f02/hw/1/graph/class-graph.cd

-- Karl Lieberherr