Some 'random' stuff.

-More comments to help me remember things.
-More ‘poor; tests for union .
-The beginnings of further testing using random BSTs if my randomBST
function works. [Which I don’t know yet.]
-Subset still seems to be an issue. [Which means equals is likely an
issue.]

-Are the specifications for difference [“Returns a set containing
everything in u except those that are in t.”] those that we should be
shooting for? Or should it ‘return a set of everything that is unique
to u and t’?