Planning Exercise
   - Given, the initial state is:  On(B, Ground), On(A, Ground), On(C,A), Clear(B) and Clear(C), and
 
   - the goal state is:  On(C, Ground), On(B, C), and On(A,B).
 
   - Show a breadth first forward search.
 
   - Show a breadth first backward search.
 
   - Show a mixed BF search.