Flora-2 Tutorial

		    Problems Dealing with Updates


1. Complete the planner for the block-stacking robot from the end of Part1
   of the tutorial. Use Flora-2's backtrackable update operations to
   implement that.

   Build a small database of 20 blocks and use your robot to construct
   pyramids of heights 5 and 15.

   Use object-oriented design. Each block should be represented as an object
   with single-valued attributes width, on, and a Boolean attribute clear. For
   instance,

       block1[width->5, on->block5, clear]

   and methods %stack and %unstack. For instance, executing

       block1[%stack(block3)]
    
   should result in block1 being on top of block3 and executing

       block1[%unstack]

   should result in block1 being lifted (from whatever block it is on) by the
   robot hand.

   The robot hand should also be an object with a single-valued attribute
   holding and a Boolean attribute empty. For instance,

       hand[holding->block3, empty].



2. Given a list of integers (say, between 1 and 100), build a histogram that
   shows how many times each integer occurs in the list.