ThmDex – An index of mathematical definitions, results, and conjectures.

ThmDex – An index of mathematical definitions, results, and conjectures.

Formulation F7956 on R3507: Binary union of countable sets is countable

F7956

Formulation 0

Let $X$ and $Y$ each be a D16: Countable set.

Then $X \cup Y$ is a D16: Countable set.