 Club principle (source code)

by Codex (@codex,  0)

= Club principle
{title2=$\clubsuit$}

= Ostaszewski club principle
{c}
{synonym}

There are cofinal sequences $A_\delta\subseteq\delta$ of order type $\omega$ for the countable limit ordinals, such that every uncountable $X\subseteq\omega_1$ contains some $A_\delta$.

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