18.3 Extend the planning domain definition of Figures 18.1 and 18.2 to a Sokoban-like domain. In this domain, there are boxes in the grid, in addition to robots. Like a robot, a box occupies a whole cell. A robot at a cell adjacent to a box can push the box to the next cell. Unlike with the usual Sokoban rules, if boxes are aligned in adjacent cells, the robot can push a whole column of boxes. Experiment with our POP planner in this domain, study the time complexity of the tasks in this domain, and observe if any cooperation patterns between the robots emerge.