I am wondering whether there exists a data structure similiar to a bloom filter in the sense that it is an approximate finite set representation (allows for false positives, but no false negatives) and supports:

- constant time complexity union of two sets
- constant time complexity insertion of an element

**but** also allows for efficient iteration over the approximate elements in the set, i.e. iterate over all elements that are either actually in the set or false positives with a time complexity that is *linear in the number of elements in the set*