ThmDex – An index of mathematical definitions, results, and conjectures.
Binary union of countable sets is countable
Formulation 0
Let $X$ and $Y$ each be a D16: Countable set.
Then $X \cup Y$ is a D16: Countable set.
Proofs
Proof 0
Let $X$ and $Y$ each be a D16: Countable set.


This is a subresult to R3506: Finite union of countable sets is countable. $\square$