I have written the Simulton, Mobile_Simlton and Prey classes, which you need to understand and use, but do not need to change. Note that the Simulton class defines a contains method that is inherited and can be overridden (and should be, in Black_Hole, which changes the meaning of containment). This method determines whether an (x, y) coordinate is inside the object by checking whether it is contained in the bounding box of each object: the bounding box is just all coordinates extending from the object's center, going half-height up and down, and half-width left and right. The Black_Hole class overrides contains to be whether an (x, y) coordinate is inside the perimeter of the object: this is a "smarter" contains that actually knows about the shape of its simulton, not just the generally useful bounding box.