You're right that if the set is of {99,100,101} then of course 100 falls into neither category and each category has cardinality 1, but we're talking about real

You're right that if the set is of {99,100,101} then of course 100 falls into neither category and each category has cardinality 1, but we're talking about real-valued variables, so I don't think that's a worry. I imagine it happens 'almost never' (except where n=1). [0] https://en.wikipedia.org/wiki/Almost_never https://en.wikipedia.org/wiki/Almost_never