I read this interesting post: Intersection of manifolds.
In geometry/topology one can consider intersection of manifolds (which need not be a manifold). I'm curious if one can do this in Semi-Riemannian geometry in a meaningful way?
Specifically I guess:
Has anyone ever studied in general, the problem of $k$ intersecting solutions to the EFE with cosmological constants?
And is there any motivation to study this?
Some extra conditions may be that the resulting structure is again a solution to the EFE. I think one would unfortunately have to drop the property of causality.