Independent sets in edge-clique graphs

We show that the edge-clique graphs of cocktail party graphs have unbounded rankwidth. This, and other observations lead us to conjecture that the edge-clique cover problem is NP-complete for cographs. We show that the independent set problem on edge-clique graphs of cographs and of distance-hereditary graphs can be solved in O(n^4) time. We show that the independent set problem on edge-clique graphs of graphs without odd wheels remains NP-complete.