“…Restrictions on the c-planarity testing problem that have been considered in the literature include: (i) assuming that each cluster induces a small number of connected components [8,4,11,10,1,2,12] (in particular, the case in which the graph is c-connected, that is, each cluster induces one connected component, has been deeply investigated); (ii) considering only flat hierarchies, where all clusters different from the root of T are children of the root [3,6]; (iii) focusing on particular families of underlying graphs [3,13]; and (iv) fixing the embedding of the underlying graph [6,12].…”