6: Cardinality
Thumbnail: Bijective function from N to the set E of even numbers. Although E is a proper subset of N, both sets have the same cardinality. (CC BY-SA 4.0; Jochen Burghardt via Wikipedia )
Thumbnail: Bijective function from N to the set E of even numbers. Although E is a proper subset of N, both sets have the same cardinality. (CC BY-SA 4.0; Jochen Burghardt via Wikipedia )