COSC 159 - Artificial Intelligence
                   Assignment #6

               Building with Blocks

               Due: Monday, April 20


GOAL: Write Prolog predicates which define operators for
stacking and unstacking blocks and demonstrate how they can
be used with the means_ends predicate (discussed in class) to
plan block-stacking tasks.

DETAILS: On pages 313 and 314 in the textbook, operators are defined
for a simple block-stacking task.  The basic assignment calls
for you to use the Prolog format presented in class to define
these operators for use with the Prolog means-ends analysis
predicate.  The directory ~mikes/159/planning on studsys
contains files such as machine.pr and flash.pr which show
how to define operators in other task settings.  Also there
are log files (log1, log2) which show how to "run" these
problems.  The file mea.pr contains the definition and supporting
predicates for the means-ends analysis.  You shouldn't need
to change anything in this file.
  Note that the book is using these operators (on p.314) for a
different type of planning (plan-space search) than we are.
Also, recall that the book is using Lisp syntax for its operators
and state descriptions, whereas we will be using Prolog syntax.

  You can simply define specific operators for every combination
of blocks which will need to be moved (this is the book's
approach), or you could use an operator schema to combine
similar operators.  A simple example of such a schema approach
for the flashlight repair task can be found in the files
flash2.pr and log3 (and was discussed in class).  Also, the
text discusses an operator schema for the block-stacking tasks
on pages 307 and 308.
  Implementing the schema will be considered "extra effort", but
you may find it's actually easier than writing out all of the
specific operators.

REQUIRED TASKS: Your code should allow you to produce plans for
the following two tasks:

Task 1: Given three blocks in the following configuration

           ---
          | C |
           ---
           ---     ---
          | A |   | B |
           ---     ---
   --------------------------
            TABLE

construct a plan which will produce the goal state

           ---
          | C |
           ---
           ---
          | A |
           ---
           ---
          | B |
           ---
   --------------------------
            TABLE

Task 2: Construct a plan which will change from the first state below
to the second

 START:                       GOAL:
                                    ---
                                   | A |
                                    ---
        ---      ---                ---
       | B |    | D |              | C |
        ---      ---                ---
        ---      ---                ---     ---
       | A |    | C |              | B |   | D |
        ---      ---                ---     ---
   ----------------------     -----------------------
           TABLE                       TABLE


Remember, you can't move blocks which have other blocks on top
of them.  Also, the book's operators require that a block be
on the table before you can put it onto another block.  If you
decide to change that requirement, be sure and document that fact.

HAND-IN: A brief written description of whatever variables or predicates
you use to describe the state, Prolog code defining the operators for
this project, and sample runs showing how means_ends can construct
plans for the two tasks given above.