Let $X_1, \dots, X_N$ each be a D16: Countable set.

Then $\bigcup_{n = 1}^N X_n$ is a D16: Countable set.

Result R3506
on D16: Countable set

*Subresult of R262: Countable union of countable sets is countable*

Finite union of countable sets is countable

Formulation 0

Let $X_1, \dots, X_N$ each be a D16: Countable set.

Then $\bigcup_{n = 1}^N X_n$ is a D16: Countable set.

Subresults

▶ | R3507: Binary union of countable sets is countable |

Proofs

Let $X_1, \dots, X_N$ each be a D16: Countable set.

This is a subresult to R262: Countable union of countable sets is countable. $\square$