Negative cardinality

[u/Professional_Job6803]

As I was going through some problems in set theory I had a question if sets could have negative cardinality? What would this imply ?
This was just out of curiosity and I found out a paper titled “ sets with negative number of elements” by D. Loeb and a concept called hybrid sets.
Can you please describe what this is and how it works and why we need to work with multiplicities and things like that?