You are to complete Exercise 3 in the chapter on learning.
The files pdp1.lisp and pdp2.lisp contain the functions for
the networks shown in Figures 10.12 and 10.13. 
You are to turn in the functions for the new network and 
the revised back propagation routines. 
In addition, you are to turn in statistics allowing 
comparison with the statistics shown in Table 10.2. 
