let intersect s t = match s.node, t.node with
| Finite s, Finite t -> E.intersect s t
| CoFinite s, Finite t -> not (E.subset t s)
| Finite s, CoFinite t -> not (E.subset s t)
let intersect s t = match s.node, t.node with
| Finite s, Finite t -> E.intersect s t
| CoFinite s, Finite t -> not (E.subset t s)
| Finite s, CoFinite t -> not (E.subset s t)