According to Michael Craig-Martin, the very ordinariness of these simple grey boxes is intended to allow the viewer to focus on ''the idea embodied in the piece''. The work is an exploration of what happens to four identical structures when a logical mathematical progression is applied to them. The lids were created by cutting away the top surface of the boxes in a sequence of 6, 12, 18 and 24 inch intervals. The artist then reversed the order of the lids, placing the first lid on the fourth box, and so on. ''With the lids reversed, the boxes are always both visually and factually unique. However, taken as a whole, the piece is still essentially 4 identical boxes,'' he has commented.