Intersection: require same number of "inside" and "outside" embeddings
Currently an Intersection
can have n₀ embeddings into grid0 and n₁ embeddings into grid₁.
However it is unclear what the semantics in the n₀ ≠ n₁ case are: how does one known what embedding into the first grid has to go with which embedding into the second grid?
I propose to require that the number of embeddings is the same for both grids.