# Thread:

1. ## stationary set

Say that a set $A \subseteq \omega_1$ is stationary if it has nonempty intersection with every subset of $\omega_1$. Suppose that there is an injection from $\omega_1$ into $\mathcal{P}(\mathbb{N})$. Show that every stationary subset of $\omega_1$ can be split into two disjoint subsets of $\omega_1$.

Notation: $\omega_1$ denotes the first uncountable ordinal. We may us the Countable Principle of Choice, but not the Axiom of Choice.
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