`type t`````
`val cutoff : t ‑> t ‑> bool`

A function for testing whether the model has changed enough to require refiring the incremental graph.

It's best if the values in the model support a semantically reasonable cutoff function which lets you avoid infinite recomputation loops that can otherwise be triggered by the visibility checks. For this reason, it's typically a good idea to avoid having simple closures stored in the model.

That said, it does work if you put phys_equal in for the cutoff.