Show that a finite subset $A \subset B$, of a countable set is also countable.
I started by saying that by definition there exists an injection $f: A \rightarrow B$
not sure what to do now, any help is appreciated!
2026-04-07 14:13:06.1775571186
Need help with countability proof
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As asked, because $B$ is countable you have an injection from $B \to \Bbb N$ As $A$ is a subset of $B$, the injection from $B$ restricted to $A$ is an injection into $\Bbb N$