Intersection Over Union

Qualitatively present the overlap of two domains.

Math and Physics have a high overlap and are very large domains in on themeselves. I need some control over how I express the closeness of two domains and be able to compare pairs with each other. Even a partial ordering is useful.

So qualitatively defining the closeness of domains based on their intersection divided by their union.

In this case, the IOU between Calculus and it's applicability to Physics should be much higher than it is for good old wholesome Mathematics and Physics as a lot of abstract branches like number theory don't have an outright obvious application to physics.