Inserted: 5 nov 2018
Last Updated: 8 nov 2018
In this paper we make the final step in finding the optimal way to enclose and separate four planar regions with equal area. In (9) the graph-topology of the optimal cluster was found reducing the set of candidates to a one-parameter family of different clusters. With a simple argument we show that the minimal set has a further simmetry and hence is uniquely determined up to isometries.