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Keywords:
ideals on countable sets; comparison game; Tukey order; games on integers
ideals on countable sets; comparison game; Tukey order; games on integers
Summary:
We propose and study a “classification” of Borel ideals based on a natural infinite game involving a pair of ideals. The game induces a pre-order $\sqsubseteq$ and the corresponding equivalence relation. The pre-order is well founded and “almost linear”. We concentrate on $F_{\sigma}$ and $F_{\sigma\delta}$ ideals. In particular, we show that all $F_{\sigma}$-ideals are $\sqsubseteq$-equivalent and form the least equivalence class. There is also a least class of non-$F_{\sigma}$ Borel ideals, and there are at least two distinct classes of $F_{\sigma\delta}$ non-$F_{\sigma}$ ideals.
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