What about the cardinality of Cartesian products? So if we have sets:
We can have the Cartesian product set:
We can see that:
\(|A\lor B| = |A|+|B|-|A\land B|\)
\(|a \setminus b|=|a|-|a\land b|\)
What about the cardinality of even numbers? Well, we can define a bijective function between each:
Similarly for odd numbers:
So these both have cardinality \(\aleph_0\).