Approach to creating recursive programs	    March 29, 1991

Step
 1.  Identify the function, F, which must be implemented and the data
     structure.
     Examples:	1. Determine the location of a data item in an array of size N.
		2. Count the number of nodes in a binary tree of size N.
		3. Solve a certain puzzle of size N.
    Note: You are free to determine how "size" is measured.

 2. Determine how to implement the function on a very small size data
    structure.  For example, a list or a binary tree of size 0 or a puzzle
    of size 1.

 3. Assume that the function can be implemented on the data structure so long
    as the size of the data structure does not exceed N-1.

 4. Determine a method of implementing the function on a data structure of
    size N by using solutions for data structures of size N-1 or smaller.


EXAMPLES:
 A. Determine the location of an element in an array of size N.
    FIND Location of data_item in array, A, of size N
	If N = 0 Then the data item in not in the array.
	Else If the data item equals the last (Nth) item in the array
	     Then Location is N
	     Else FIND Location of data_item in array, A, of size N-1.

 B. Count the number of nodes in a binary tree of size N.
    COUNT Number_of_Nodes in binary tree, B, of size N.
	  (where N is the number of levels in B)
    If N = 0 Then Number_of_Nodes = 0
    Else COUNT Number_of_NodesL in the left subtree of B (size<=N-1)
	 COUNT Number_of_NodesR in the right subtree of B (size<=N-1)
	 The Number_of_Nodes in B equals the Number_of_Nodes in the left
	 subtree of B plus the Number_of_Nodes in the right subtree of B
 	 plus 1 (the root of B).  i.e.
	 Number_of_Nodes = Number_of_NodesL + Number_of_NodesR + 1

	Note that Number_of_NodesL and Number_of_NodesR are recursive calls to Number_of_Nodes
	with the left and right subtrees as parameters.