To be slightly clearer, the values here are Urbit "nouns." A noun is an atom or a cell. An atom is an unsigned integer of any size. A cell is an ordered pair

To be slightly clearer, the values here are Urbit "nouns." A noun is an atom or a cell. An atom is an unsigned integer of any size. A cell is an ordered pair of nouns. I am fairly confident that many useful sets can be specified as the fixpoint set of a function in this space.