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Two-player turn-based perfect-information games, surreal numbers, impartial games and Sprague-Grundy theory, partizan games

14 votes
1 answer
560 views

Is there an elementary proof of a better result for the finite guessing-box puzzle?

The infinitary guessing-box puzzle is amazing — see here. In the basic form, the Guessing-box Hall has infinitely many wooden boxes, each containing a real number, and there are 100 mathematicians wh …
Joel David Hamkins's user avatar
34 votes
7 answers
3k views

A hat puzzle question—how to prove the standard solution is optimal?

I am currently writing an essay on hat puzzles, and for the warm-up section I introduce some of the standard finite hat puzzles. One of these proceeds as follows: You and two friends are each given a …
Joel David Hamkins's user avatar
7 votes

Negative of combinatorial game

No, the negative a game is simply the game in which the player's roles are swapped, hereditarily. You can see this in the definition you provided $$-G=\{ -G^R\mid -G^L\}$$ since the left options in $- …
Joel David Hamkins's user avatar
6 votes
Accepted

Uniform strategy on Kastanas' game

This is a great question — definitely enjoyed. Assuming the axiom of choice, then the answer is yes. Theorem. Assume there is a well ordering of the real numbers. If player I has a winning strategy, t …
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, …
Joel David Hamkins's user avatar
9 votes

JUSTICE & INJUSTICE — two 2-player finite games

Here is a complete winning strategy for the Justice game. One wins the Justice game simply by following the usual Nim strategy, with all the same winning positions and moves (except if the position is …
Joel David Hamkins's user avatar
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 …
Joel David Hamkins's user avatar
54 votes
1 answer
3k views

In the two-person Killing the Hydra game, what is the winning strategy?

My question is which player has a winning strategy in the two-player version of the Killing the Hydra game? In their amazing paper, Kirby, Laurie; Paris, Jeff, Accessible independence results for P …
Joel David Hamkins's user avatar
19 votes
2 answers
3k views

What is the winning strategy in this pebble game?

Consider the following two-player pebble game. We have finitely many stones on a finite linear track of squares. We take turns, and the allowed moves are: move any one stone one square to the left, …
Joel David Hamkins's user avatar
3 votes
Accepted

Is following function a metric on the set of isomorphism classes of graphs with countably ma...

To prove that this is a metric, consider the following theorem. Theorem. If the second player can survive for $n$ steps in the $(\Gamma_1,\Gamma_2)$ game, and for $m$ steps in the $(\Gamma_2,\Gamma_3 …
Joel David Hamkins's user avatar
4 votes

Combinatorial games with infinite paths, and generalized Sprague-Grundy theory

I am not sure what you imagine, but once one makes the move to games with infinite play, then various set-theoretic issues come to light, and the subject becomes more set-theoretic and less like combi …
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
16 votes

Alice and Bob playing on a circle

For even $n$, I claim that nobody has a winning strategy, and therefore both players have drawing strategies. To see this, observe first that by the fundamental theorem of finite games, we know that …
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 …
Joel David Hamkins's user avatar

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