Game-theoretic variants of splitting number

TL;DR

This paper introduces game-theoretic variants of the splitting number, defining six related cardinal invariants, and investigates their relationships and differences, revealing new insights into their behavior and consistency.

Contribution

It defines three types of infinite games related to the splitting number and introduces six cardinal invariants, analyzing their values and relationships, including consistency results.

Findings

Three invariants equal the continuum size

One invariant equals the σ-splitting number

Two invariants are consistently different from classical invariants

Abstract

We consider combining the definition of a cardinal invariant and the notion of an infinite game. We focus on the splitting number $\mathfrak{s}$ since the corresponding cardinal invariants behave in an interesting way. We introduce three kinds of games as reasonable realizations of the combination of the notions of splitting and infinite games. Then, we consider two cardinal invariants for each game, so we define six numbers. We prove that three of them are equal to the size of the continuum $\mathfrak{c}$ and one of them is equal to the $\sigma$-splitting number $\mathfrak{s}_\sigma$, which is defined as the minimum size of a $\sigma$-splitting family. On the other hand, we show that the remaining two numbers are consistently different from $\mathfrak{c}$, $\mathfrak{s}$ and $\mathfrak{s}_\sigma$. Moreover, though the two numbers share almost the same rule of the game, we prove that they can take distinct values from each other, and hence the slight difference of the rule is actually crucial in this sense.