  The other thrust had to do with the conceptual points made in Section 4.5. The idea is to situate the mathematics of set theoretic circularity inside a larger topic, coalgebra, and then to understand both points in terms of a larger division between “bottom-up” and “top-down” ideas.  This larger discussion is more programmatic than we would like, and much remains to be done on it.  Our hope is that it helps readers understand set theoretic circularity, both how it works, and also why it is attractive.