Exercise
   - Let's try one perceptron with two inputs.  If the first has a weight
       of 2, and the second a weight of -3, what is the input to perceptron
       for 4,5?
 
   - for 1,-5.
 
   - If there is a linear transfer function of -2, what's the output?
 
   - If there is a step transfer function at 0, what's the output.
 
   - Now make a second perceptron with weights -7 and 10.  What are its
     inputs.       
 
   - If these in turn are connected to a second layer with weights of
       -4 and -2, what are the second layer's inputs?
 
   - If it's a linear transfer function with value -3, what's the output?
 
   - How would you solve the xor problem?