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Infinite games. Combinatorial game theory for infinite two-player games of perfect information. Open games, clopen games. Determinacy. Transfinite game values. Topological games.

19 votes

Examples of concrete games to apply Borel determinacy to

The game of infinite Hex, proceeding from an arbitrary position, is a good example with all the features you seek. The game was the subject of my Oxford student Davide Leonessi's masters MFoCS dissert …
Joel David Hamkins's user avatar
24 votes
2 answers
1k views

What is the complexity of the winning condition in infinite Hex? In particular, is infinite ...

Consider the game of infinite Hex, where two players Red and Blue alternately place their stones on the infinite hex grid, each aiming to create a winning configuration. Red wins after infinite play, …
11 votes

Strategic vs. tactical closure

The answer to the topological version of Banach-Mazur games is negative, proved by Gabriel Debs in 1985: Debs, Gabriel, Stratégies gagnantes dans certains jeux topologiques (Winning strategies in cer …
Joel David Hamkins's user avatar
7 votes

Strategic vs. tactical closure

For a partial answer, let me prove that every strategically closed partial order admits a nearly tactical winning strategy, one that depends only on the previous two moves, that is, on the previous mo …
Joel David Hamkins's user avatar
9 votes
3 answers
1k views

The Sudoku game: Solver-Spoiler variation

Consider the Sudoku Solver-Spoiler game, a natural variation of the Sudoku game recently appearing in the question Who wins two-player Sudoku? posted by user PyRulez. In that game, the players attempt …
25 votes
4 answers
2k views

The Chocolatier's game: can the Glutton win with a restricted form of strategy?

I have a question about the Chocolatier's game, which I had introduced in my recent answer to a question of Richard Stanley. To recap the game quickly, the Chocolatier offers up at each stage a finite …
23 votes
Accepted

An infinite game possibly due to Ernst Specker

I don't know about the game attributed to Specker, but here is a simple game with your desired features. Let us call it the Chocolatier's game. There are two players, the Chocolatier and the Glutton. …
Joel David Hamkins's user avatar
2 votes

How to describe the common boundaries between regions in a infinite Sudoku?

Thanks for your kind words about my blog. In the general-size square Sudoku board, you have an $\kappa\times\kappa$ array of $\kappa\times\kappa$ local blocks for some (possibly infinite) cardinal $\ …
Joel David Hamkins's user avatar
38 votes
Accepted

Is there a position in infinite Go for which the life of a particular stone has transfinite ...

This is a really great question! Previous attempts to make sense of infinite Go have sometimes had problems because it wasn't clear how to define the winner of a game of Go after transfinite play. T …
Joel David Hamkins's user avatar
19 votes
3 answers
1k views

The arithmetic progression game and its variations: can you find optimal play?

Consider the arithmetic progression game, a two-player game of perfect information, in which the players take turns playing natural numbers, or finite sets of natural numbers, all distinct, and the fi …
65 votes
Accepted

A game on integers

I claim that Player A has a winning strategy in your game, and furthermore, it is a winning strategy for her simply to play the smallest available number. Let me consider the game along with several …
Joel David Hamkins's user avatar
58 votes
Accepted

Does knight behave like a king in his infinite odyssey?

Consider the following open knight's tour on a $5\times 5$ board, starting at position $1$ and then touring the $5\times 5$ board in the indicated move order. The final position is $25$, from which th …
Joel David Hamkins's user avatar
4 votes

Products and Gale-Stewart games

It is a very nice question. I claim that it is not sufficient that $C$ is determined, and indeed, there are counterexamples where $C$ is a game with only two moves. Consider the two-dimensional gam …
Joel David Hamkins's user avatar
13 votes
Accepted

Choosing subsets of $\mathbb R$ of cardinality $\frak c$, who wins?

In ZFC, the player aiming for the empty set has a winning strategy in the game played on any infinite set, including the reals. Using the axiom of choice, we can well-order the set and thereby pretend …
Community's user avatar
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6 votes

Determinacy of (infinite, possibly loopy) combinatorial games

This amounts to the Gale-Stewart theorem showing that open games are determined. The issue of draws can be easily finessed, as I explain below. Specifically, a game of perfect information is open for …
Joel David Hamkins's user avatar

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