CSCE 625
Homework Assignment #7
due: Tues, 11/17/09

There are 3 rooms arranged as below, with a door d1 between rooms
r1 and r2, and door d2 between r2 and r3.  Initially, the robot is in
room, and there are two boxes, b1 and b2, in room r2.  The goal is to
get both boxes in r3.  The robot can only push one box at a time.

   ----------------------------------------------
   |             |     box b1      |            |
   |             \ d1           d2 \            |
   |   robot     |     box b2      |            |
   ----------------------------------------------
      room r1          room r2         room r3

1. Write the STRIPS operators for the actions GoThru(D,X,Y) and
PushThru(B,D,X,Y), where D is a door B is a box, and X and Y are
rooms.  (Remember, a STRIPS operator has pre-conditions, an add list,
and a delete list.)

2. Solve the above problem (i.e. make a plan) using goal-regression.
At each step, underline the sub-goal being achieved by the action
selected.  State the final sequence of actions derived.

3. Solve the problem using partial-order planning.  Show the plan
graph with all causal links (use solid arrows) and ordering
constraints (use dashed arrows) properly annonated (including
inputs/pre-conds and outputs/effects of each node).  List all
linearization(s).