We consider various approaches of linking the underlying bicategory with the newly constructed ones, eg, by means of two-dimensional generalizations of bifibrations. In the quest for a better connection, we investigate, whether Chu-spans form a double category. While this turns out not to be the case, we are led to considering a generalization of the construction to paths of 1-cells in the base, leading to two hierarchies of closed bicategories, one for linear paths and one for loops. The possibility of moving beyond paths, respectively, loops of the same length is indicated.
Finally, Chu-spans in rel correspond to bipartite state transition systems. Even though their composition may fail here due to the lack of pullbacks in rel, basic game-theoretic constructions can be performed on cyclic Chu-spans. These are available in all symmetric monoidal closed categories with finite products. If pullbacks exist as well, the bicategory of cyclic Chu-spans inherits a monoidal structure that on objects coincides with the categorical product.