/*
    This is an example of a tic tac toe board.  
    It is also test case 1 for Homework 5.

    The meaning of the location constants are as follows:

        upper,left   | upper,central   | upper,right
        -------------------------------------        
        central,left | central,central | central,right
        -------------------------------------        
        lower,left   | lower,central   | lower,right

    You are x and the opponent is o.

    This particular board is:

        x | o | o
        ---------
        x | o | 
        ---------
        x |   | 
*/

      square(upper, left, x) :- .
      square(upper, central, o) :- .
      square(upper, right, o) :- .

      square(central, left, x) :- .
      square(central, central, o) :- .
      square(central, right, unoccupied) :- .

      square(lower, left, x) :- .
      square(lower, central, unoccupied) :- .
      square(lower, right, unoccupied) :- .