Imagine two two-dimensional (2D) boxes containing two hard discs. In each, two hard disks differ in diameter (Fig. ). Assume, in one box, the larger particle is fixated adjacent to the wall, and the smaller particle is distributed in the residual space -in discretely partitioned squares with the dimensions equal to the diameter of the small particle (Fig. ). Now, imagine in the other box, the smaller particles are fixed adjacent to the wall, and the larger particle is distributed in the residual space of the box -in discretely partitioned squares with the dimension equal to the diameter of the larger particle (Fig. ).