An Effective Proof that Open Sets are Ramsey

1996-01-22T00:00:00Z (GMT) by Jeremy Avigad
<p>Solovay has shown that if O is an open subset of P(ω) with code S and no infinite set avoids O , then there is an infinite set hyperarithmetic in S that lands in O . We provide a direct proof of this theorem that is easily formalizable in ATR<sub>0</sub> .</p>

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