Finite-condition Lévy collapse ($\mathrm{Lv}(\kappa )$)

The finite-condition Lévy collapse $\mathrm{Lv}(\kappa )$ consists of finite partial functions $p$ with $\mathrm{dom}p\subseteq \kappa \times \omega$ and $p(\alpha ,n)<\alpha$, ordered by reverse inclusion. The generic union gives a surjection $\omega \to \alpha$ for every infinite $\alpha <\kappa$. If $\kappa$ is regular and uncountable, the Delta-system lemma at a regular uncountable cardinal proves the $\kappa$-chain condition, so the extension makes $\kappa ={\aleph }_1$.