feat : define cocountable and cocardinal filters
Define cocountable and cocardinal filters.
Any feedback on the way these are phrased and written is more than welcome!
#10531 defines CardinalInterFilter, I'll make sure that both PRs use similar design choices. I believe it should be possible at some point to conclude that cocardinal filters (cardinality c) are CardinalInterFilters for all cardinalities strictly lower than c.
I've removed the 'Awaiting-Review' label for now, as I'll first build up the theory of CardinalInterFilters more, these were introduced in #10531. Once this is finished, this PR will also include proofs that cocardinal filters have certain CardinalInterFilter properties.
This PR has been closed in favour of a newer PR, which makes better use of the recently added CardinalInterFilter file.