# Questions tagged [combinatorial-game-theory]

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

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### A combinatorial game with seemingly curious arithmetic properties

We consider the following combinatorial game (with two players
alternatively playing optimally). Posititions are given by heaps containing $b\geq 0$ black and $w\geq 0$ white stones and are
encoded by ...

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2
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### A little number theoretic game

I came up with this little two player game:
The players take turns naming a positive integer. When one player says the number n, the other player can only reply in two different ways: They can either ...

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0
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### Eventual stabilization for repeatedly adding multiplayer games

This question is an outgrowth of a couple previous questions of mine. In order: 1,2,3. This should be fully self-contained, but those questions may help motivate this one.
To keep things readable, I'...

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### Monoid associated to $>2$-player Hackenbush

There is some literature on multiplayer combinatorial game theory, but as far as I can tell none of it follows the line of attack below. I'd love a pointer to a similar approach taken in the ...

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### What is the complexity of the winning condition in infinite Hex? In particular, is infinite Hex a Borel game?

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, ...

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### A question about a theorem in ONAG by Conway

Does anyone here know about Conway's On numbers and games? Because I can't figure out what he does here on p18. It feels a bit like he's using the statement we want to prove
I will type the proof ...

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### Projective plane finite game

This is a 2-person game.
Let $\ P\ $ be any arbitrary projective space (of any dimension $\ \ge2$ and any cardinality, etc., but typically, let it be a finite plane over a field). Let $\ S_0\subseteq ...

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### JUSTICE & INJUSTICE — two 2-player finite games

There is a non-empty finite set $\ K,\ $ say, of plates. Initially, there are $\ p_0(k)\ $ stones on the $k$-th plate, where
$\ p_0(k)\in\mathbb Z_{_{\ge0}}\ $ for each $\ k\in K.$
So far, it is like ...

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0
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### Fast algorithm to compute nimber product

It is known that nimbers (Grundy numbers) below $2^{2^n}$ form a field with the nim addition $\oplus$ and the nim product $\cdot$.
Generally, one can develop an algorithm to compute the product of two ...

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### Set theory / Formal logic of Baba is You

''Baba is You'' is a recent puzzle game in which the player builds a set of rules by pushing squares with words written on them. If we leave aside the combinatorial difficulty of how to move the ...

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### Euclid's algorithm as a combinatorial game

Consider the following two player game based on the Euclidean algorithm: Positions are given by $(a,b)$ in $\mathbb N^2\setminus\{(0,0)\}$ (where $\mathbb N=\{0,1,2,\ldots\}$) defining a greatest ...

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### Two-player item picking game

Two players $A$ and $B$ play this game: There are $n$ items, where the $i$th item is of value $a_i$ to player $A$ and is of value $b_i$ to player $B$. Two players take turns picking items, and each ...

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### Strategy-stealing in chess

Is it proved that white can guarantee at least draw in chess?
A while ago I was told that it was proved using strategy-stealing, but I cannot find a reference.
Postscript. Please accept my apology ---...

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### Do restricted Nim-like games have winning strategies?

Considering a Nim-like game to be:
There are three piles $A,B,C$, and the amount of their elements are $|A|=2, |B|=5, |C|=6$;
There are 2 players. Each time a player can either take $x (1\leq x \leq ...

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### What does it mean for the surreal numbers/partizan games to be "universally embedding"?

In "On numbers and games", Conway writes that the surreal Numbers form a universally embedding totally ordered Field. Later Jacob Lurie proved that (the equivalence classes of) the partizan ...

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### Does Conway’s field of finite nim values have arithmetically tractable isomorphisms?

Conway constructed a field of characteristic 2 whose elements are the finite Nim values, indexed by the natural numbers. What is known about nontrivial automorphisms of this field? Do any of them ...

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### The maximum number of moves in a game of Nim [closed]

I was assigned a fun, but also quite hard problem for my computer science class - I have to write a java program that computes the maximum number of turns in an optimal game of Nim.
In case you are ...

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### Why is game theory formulated in terms of equilibrium instead of winning strategies?

Game theory, on the outset, seems to invite the questions,
"what can I do to win" or "how do I beat my opponent?"
So many people who are not familiar with game theory look to game ...

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### Name of a game : Remove two chips from a vertex or one chip from both ends of an edge

Consider a finite graph $\Gamma$ with a positive number $n_v\geq 0$ of chips stacked at each vertex $v$ of $\Gamma$. Two players play in turn with moves consisting either of removing two chips from a ...

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### Who wins this two player game of making squares?

Two players take turns coloring edges on an $n$-by-$n$ grid. Both players use the same color. Every time a player surrounds a square of the grid, they mark that square with their name and go again. ...

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### Name for an easy combinatorial game

What is the name of the following combinatorial game:
Two players, moving in turn.
Positions: $0,1,2,\ldots$.
Moves: $n\longmapsto n-1$ or $n\longmapsto \lfloor n/2\rfloor$
if $n>0$.
No move for $0$...

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### A game based on the Euclidean algorithm

The following game is based on a somewhat "stupid" version of the Euclidean algorithm (where we allow only subtractions).
Positions are given by finite non-empty multisets (repeated elements ...

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1
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### Complexity of games with graph classes

Let $\mathfrak{G}$ be the class of all finite directed and undirected graphs. Let $A,B\subseteq \mathfrak{G} $, $A$ and $B$ are closed under graph isomorphisms, and $A \cap B = \varnothing$. Consider ...

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### 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 ...

0
votes

1
answer

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### Mapping problem reminiscent of Mastermind

Given 2 finite sets $S$ and $M$, with $\operatorname{card}(S) \geq \operatorname{card}(M)$, and an item $z \not\in M$. There is an unknown function $f: S \to M \cup \{z\}$, which is known to be one-to-...

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### Winning moves in Hex

The game "Hex" is a simple game which apparently has been invented at least twice (Piet Hein and John Nash). The game consists of an n by n grid of hexagons, with two opposite sides marked ...

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### Tic-tac-toe with one mark type

Parameters $a,b,c$ are given such that $c\leq\max(a,b)$. In an $a\times b$ board, two players take turns putting a mark on an empty square. Whoever gets $c$ consecutive marks horizontally, vertically, ...

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### Winning criterion for a combinatorial game

Given $n$,
let $\mathcal{R}$ be a set of pairs $(\rho,A)$
where $A\subseteq n, \rho\in 2^A$.
Consider the following game between A and B.
At each round $t$, A enumerates an $m\in n$ (that has not been ...

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### What values are representable by Hackenbush stalks?

It is known that every number can be represented by some red-blue Hackenbush stalk (see here, for instance). What values can be represented by red-blue-green Hackenbush stalks? In addition, what games ...

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### Nim variant with minimum number of objects?

I'm wondering where I can find in the literature (if it exists) a discussion of a Nim variant where we impose the additional condition on Nim that we can remove only up to $c$ objects before the game ...

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### A "Markov game"

I call games similar to the one I describe below to be Markov games. I am selecting just that one or rather a 1-parameter series of games. The open challenge is to find out which of the players $\ 0\ $...

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1
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### An averaging game on finite multisets of integers

The following procedure is a variant of one suggested by
Patrek Ragnarsson (age 10). Let $M$ be a finite multiset of
integers. A move consists of choosing two elements
$a\neq b$ of $M$ of the same ...

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### Quantum surreal numbers

Toward Quantum Combinatorial Games presents the definition of a "quantum game", allowing a superposition of moves rather than a single classical move. This leaves me wondering: Since surreal ...

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### pursuit-evasion based on Schroeder's upper bound for graphs of genus $g$

I am following Schroeder's work on pursuit-evasion games on graphs (often called "cops and robbers"). In his 2001 publication ("The copnumber of a graph is bounded by $\lfloor 3/2 {\ \...

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### Players alternate moving a $\{\swarrow,\uparrow,\rightarrow\}$ piece on a chessboard

Edit $4.$ $-$ Proposing to reopen the question (the related competition should be over by now).
Edit $3.$ $-$ I have just found out that the linked competition (see the "Edit $1$.") is still ...

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### Does the Angel have to be really smart?

My question is about the computational complexity of the Angel's strategy in the Angels and Devils game, tl;dr does the Angel have a polynomial time strategy.
I'm a big Conway fan, so as you can ...

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### How does Conway's proposed compromise for constructing the real numbers in ONAG actually work?

I have also asked this question on Math Stack Exchange (link).
In On Numbers and Games, after discussing the inclusion of the real numbers in the surreal numbers, No, Conway discusses the merits of ...

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### In theory, how would Oneiric numbers be defined?

Background I am not a professional mathematician. I am researching Surreal numbers & games for fun (I think they are truly beautiful). If this question is not appropriate here, I beg forgiveness &...

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### 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 ...

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### Free category with product and coproduct

Is there a known description of the free category with both product and coproduct?
That is, given a small category $C$, I want to consider a category $U C$ which has product and coproduct, a functor $...

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### Are Conway's combinatorial games the "monster model" of any familiar theory?

This is related to this question about a "mother of all" groups, and so seemed like it'd fit in better at MO than MSE.
If I understand the answer to that question correctly, the surreal numbers have ...

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### Infinite positions in 3D chomp

I've recently come back to investigating ordinal chomp. See A winning move for the first player in $3 \times 3 \times \omega$ Ordinal Chomp for a definition. I made a new discovery, that the position \...

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### Nimber $2^{2^k} - 1$ is a multiplicative generator of $[2^{2^k}]$?

Let $t = 2^{2^k}$, and consider the field $[t]$ of nimbers below $t$. For $k \leq 6$ one can check that $t - 1$ (in the usual arithmetic sense) is a multiplicative generator of $[t] \backslash \{0\}$. ...

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### 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, ...

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0
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### Suggestions for two-choice game played in ladder graph

I was just working on counting all the possible Nash Equilibrium solutions for a two-choice game played on a ladder graph (I got my results and all that for a generic number of players).
And I was ...

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### Is following function a metric on the set of isomorphism classes of graphs with countably many vertices?

Suppose $\Gamma_1(V_1, E_1)$ and $\Gamma_2(V_2, E_2)$ are simple graphs with countably many vertices. And suppose $A_1$ and $A_2$ are initially empty sets. Suppose two players play the following game: ...

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### Is Domineering on any finite approximation of the Sierpinski Carpet always a second-player win?

The game of Domineering can be played on any board consisting of some subset of $\mathbb{Z} \times \mathbb{Z}$.
In particular, consider the boards $K_n$ generated by iterating the following inductive ...

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### Perturbation of the value of a general-sum game at a equilibirium

Consider a general-sum game with $N$ players. Let $u_i(a_1, \ldots, a_N)\colon \prod_{i=1}^N A_i \rightarrow \mathbb{R} $ be the payoff of the player $i\in \{ 1, \ldots, N \}$ when each player takes ...

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### Solution to simple mathematical game

Consider the following game (that I made up). Two players each attempt to name a target number. The first player begins by naming 1. On each subsequent turn, a player can name any larger number that ...

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### Is this representation of Go (game) irreducible?

This post is freely inspired by the basic rules of Go (game), usually played on a $19 \times 19$ grid graph.
Consider the $\mathbb{Z}^2$ grid. We can assign to each vertex a state "black" ($b$), "...