Review for Test#1
  Recursion
  Recursion trees
  The situations suitable/unsuitable for recursion
  Recursive sorts (Quick will be the important one)
  BNF notations
  drawing parse trees
  Binary tree definitions, traversals.
  Existing definitions of nodes, leaf nodes, branches, 
children, two tree, complete tree, perfectly balanced 
tree
  Contiguous representation of a binary tree