6. How dense can a disc be in its Voronoi cell?
We want to show that a disc take up no larger proportion of the area in its Voronoi cell than it does in its circumscribing regular hexagon. To show this, we partition the cell into sub-regions of different types.
Suppose we now look at a cell in a layout.Draw the circumscribing circle as well, or at least itsintersection with the cell. Where it extends beyondthe cell, the line cut off by the cell boundarywill be the bisector of the rhombus associated to two discs whose hexagonally circumscribed circles intersect.
We can now divide up the cellinto distinct regions of three types: