Remark 4.7.3.11. Let $\kappa $ be an infinite cardinal. Then $\kappa $ is regular if and only if the collection of $\kappa $-small sets is closed under $\kappa $-small coproducts (this is a special case of Corollary 4.7.3.8).
$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$