sage: H = Graph({0:[1,3,5,4],1:[0,2,3],2:[1,4,5],3:[0,1],4:[0,2,5],5:[0,2,4]})

This gives me an ValueError: Graph on 6 vertices has been modified and the embedding is no longer valid. What I expect to get is a list like the one I used to define H, but with the neighbors ordered clockwise.