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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
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
7 votes

Who wins infinite Hex?

This doesn't answer the question that was asked, but rather an alternative kind of infinite Hex, played on the infinite hexagonal lattice board as shown below. I am posting it because people intereste …
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
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
16 votes

Who first chose the names Alice and Bob for players A and B?

Allow me to mention that since the players in effect adopt the roles of the quantifiers $\forall$ and $\exists$, as Bob has a winning strategy just in case for every move for Alice, there is a reply b …
Joel David Hamkins's user avatar
20 votes
Accepted

Forcing and Family Contentions: Who wins the disputes?

I like this question a lot. It provides an interesting way of talking about some of the ideas connected with the maximality principle and the modal logic of forcing. Let me make several observations. …
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
4 votes

When is a game tree the game tree of a board game?

Here is one possible answer. An essential feature of any board game, in the way I am thinking about it, is that there are only finitely many game states that are realizable on the board. This fact, co …
Joel David Hamkins's user avatar
19 votes
5 answers
1k views

When is a game tree the game tree of a board game?

This question arises from what I find interesting in the recently asked question What is a chess piece mathematically? My answer to that question was that mathematically, game pieces are in general e …
Joel David Hamkins's user avatar
14 votes
Accepted

Determined, finite games

There are numerous proofs of what I call the fundamental theorem of finite games. Theorem. (Fundamental theorem of finite games) In any finite two-player game of perfect information, one of the pla …
Joel David Hamkins's user avatar
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
0 votes

Are sums of 0-1 Pareto efficient vectors Pareto efficient?

Unless I have misunderstood, here is a counterexample. Let $A$ be the $2\times 2$ identity matrix. This has your Pareto property on $x-y$, but if $x=[{a\atop b}]$, then $Ax=x$, and there is no way to …
Joel David Hamkins's user avatar
11 votes
Accepted

Explicit examples of undetermined games

Here is an amusing concrete non-determined game, under the assumption that the dependent choice principle fails. Assume DC fails. This means that there is a set $X$ and a binary relation $R$ on $X$, …
Joel David Hamkins's user avatar
6 votes

$n$-in-a-row game on $\mathbb{R}^2$

I'll start things off by observing that this is what is known as an open game, since if player 1 wins, then the winning condition is satisfied after finitely many moves. It follows by the Gale-Stewart …
Joel David Hamkins's user avatar

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