Kerodon

$\Newextarrow{\xRightarrow}{5,5}{0x21D2}$ $\newcommand\empty{}$
$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$

Example 4.7.3.3. Let $\aleph _1$ denote the first uncountable cardinal (Example 4.7.2.12). Then a set $S$ is $\aleph _1$-small if and only if it is countable.