TITLE: Has negative cardinality been considered?
QUESTION [12 upvotes]: I'm not a set theorist. Perhaps the answer to my question is so well known that it is not appropriate to answer here or my question is absurd. Nevertheless I'll try: I have heard the rumor that, similar to the extension of positive integers to negative integers, recently(?) also attempts have been made to investigate negative cardinalities.
My question: What would be the intuitive picture behind negative cardinality and can also in that domain countable and uncountable cardinals exist?

REPLY [3 votes]: See here.
More specifically, see here.