An Extension of the Normal Play Convention to NN-player Combinatorial Games

We examine short combinatorial games for three or more players under a new play convention in which a player who cannot move on their turn is the unique loser. We show that many theorems of impartial and partizan two-player games under normal play have natural analogues in this setting. For impartial games with three players, we investigate the possible outcomes of a sum in detail, and determine the outcomes and structure of three-player Nim.Comment: 45 pages; Presented at Integers Conference 2018, submitted to Proceeding

Partizan Kayles and Misere Invertibility

The impartial combinatorial game Kayles is played on a row of pins, with players taking turns removing either a single pin or two adjacent pins. A natural partizan variation is to allow one player to remove only a single pin and the other only a pair of pins. This paper develops a complete solution for "Partizan Kayles" under misere play, including the misere monoid all possible sums of positions, and discusses its significance in the context of misere invertibility: the universe of Partizan Kayles contains a position whose additive inverse is not its negative, and, moreover, this position is an example of a right-win game whose inverse is previous-win

The Combinatorial Game Theory of Well-Tempered Scoring Games

We consider the class of "well-tempered" integer-valued scoring games, which have the property that the parity of the length of the game is independent of the line of play. We consider disjunctive sums of these games, and develop a theory for them analogous to the standard theory of disjunctive sums of normal-play partizan games. We show that the monoid of well-tempered scoring games modulo indistinguishability is cancellative but not a group, and we describe its structure in terms of the group of normal-play partizan games. We also classify Boolean-valued well-tempered scoring games, showing that there are exactly seventy, up to equivalence.Comment: 60 pages, 21 figure

Restricted developments in partizan misere game theory

Much progress has been made in misere game theory using the technique of restricted misere play, where games can be considered equivalent inside a restricted set of games without being equal in general. This paper provides a survey of recent results in this area, including two particularly interesting properties of restricted misere games: (1) a game can have an additive inverse that is not its negative, and (2) a position can be reversible through an end (a game with Left but not Right options, or vice versa). These properties are not possible in normal play and general misere play, respectively. Related open problems are discussed

Mis\`ere canonical forms of partizan games

We show that partizan games admit canonical forms in mis\`ere play. The proof is a synthesis of the canonical form theorems for normal-play partizan games and mis\`ere-play impartial games. It is fully constructive, and algorithms readily emerge for comparing mis\`ere games and calculating their canonical forms. We use these techniques to show that there are precisely 256 games born by day 2, and to obtain a bound on the number of games born by day 3.Comment: 12 page

Infinite cyclic impartial games

We define the family of {\it locally path-bounded} digraphs, which is a class of infinite digraphs, and show that on this class it is relatively easy to compute an optimal strategy (winning or nonlosing); and realize a win, when possible, in a finite number of moves. This is done by proving that the Generalized Sprague-Grundy function exists uniquely and has finite values on this class.Comment: To appear in Proc. Computer Games 199

Cumulative Games: Who is the current player?

Combinatorial Game Theory (CGT) is a branch of game theory that has developed almost independently from Economic Game Theory (EGT), and is concerned with deep mathematical properties of 2-player 0-sum games that are defined over various combinatorial structures. The aim of this work is to lay foundations to bridging the conceptual and technical gaps between CGT and EGT, here interpreted as so-called Extensive Form Games, so they can be treated within a unified framework. More specifically, we introduce a class of $n$-player, general-sum games, called Cumulative Games, that can be analyzed by both CGT and EGT tools. We show how two of the most fundamental definitions of CGT---the outcome function, and the disjunctive sum operator---naturally extend to the class of Cumulative Games. The outcome function allows for an efficient equilibrium computation under certain restrictions, and the disjunctive sum operator lets us define a partial order over games, according to the advantage that a certain player has. Finally, we show that any Extensive Form Game can be written as a Cumulative Game.Comment: 54 pages, 4 figure

The strange algebra of combinatorial games

We present an algebraic framework for the analysis of combinatorial games. This framework embraces the classical theory of partizan games as well as a number of misere games, comply-constrain games, and card games that have been studied more recently. It focuses on the construction of the quotient monoid of a game, an idea that has been successively applied to several classes of games.Comment: 21 page

Finding Golden Nuggets by Reduction

We introduce a class of normal play partizan games, called Complementary Subtraction. Let $A$ denote your favorite set of positive integers. This is Left's subtraction set, whereas Right subtracts numbers not in $A$. The Golden Nugget Subtraction Game has the $A$ and $B$ sequences, from Wythoff's game, as the two complementary subtraction sets. As a function of the heap size, the maximum size of the canonical forms grows quickly. However, the value of the heap is either a number or, in reduced canonical form, a switch. We find the switches by using properties of the Fibonacci word and standard Fibonacci representations of integers. Moreover, these switches are invariant under shifts by certain Fibonacci numbers. The values that are numbers, however, are distinct, and we find a polynomial time bit characterization for them, via the ternary Fibonacci representation.Comment: 28 page

Equality Classes of Nim Positions under Mis\`ere Play

We determine the mis\`{e}re equivalence classes of Nim positions under two equivalence relations: one based on playing disjunctive sums with other impartial games, and one allowing sums with partizan games. In the impartial context, the only identifications we can make are those stemming from the known fact about adding a heap of size 1. In the partizan context, distinct Nim positions are inequivalent.Comment: 10 pages, LaTeX; fixed typos, improved formatting consistency, added section on transfinite Ni