A Generalized Diagonal Wythoff Nim

TL;DR

This paper investigates a family of two-pile take-away games called Generalized Diagonal Wythoff Nim, exploring how the set of P-positions behaves when extending Wythoff Nim with generalized diagonal moves, and provides proofs for specific cases.

Contribution

It introduces the concept of generalized diagonal moves in Wythoff Nim and proves conjectures about the structure of P-positions for certain parameter pairs.

Findings

Proved the conjecture for (p,q) = (1,2) (splitting pair).

Established conditions under which the ratio of P-position coordinates converges to the golden ratio.

Included experimental data to guide future research on GDWN games.

Abstract

In this paper we study a family of 2-pile Take Away games, that we denote by Generalized Diagonal Wythoff Nim (GDWN). The story begins with 2-pile Nim whose sets of options and $P$-positions are $\{\{0,t\}\mid t\in \N\}$ and $\{(t,t)\mid t\in \M \}$ respectively. If we to 2-pile Nim adjoin the main-\emph{diagonal} $\{(t,t)\mid t\in \N\}$ as options, the new game is Wythoff Nim. It is well-known that the $P$-positions of this game lie on two 'beams' originating at the origin with slopes $\Phi= \frac{1+\sqrt{5}}{2}>1$ and $\frac{1}{\Phi} < 1$. Hence one may think of this as if, in the process of going from Nim to Wythoff Nim, the set of $P$-positions has \emph{split} and landed some distance off the main diagonal. This geometrical observation has motivated us to ask the following intuitive question. Does this splitting of the set of $P$-positions continue in some meaningful way if we, to the game of Wythoff Nim, adjoin some new \emph{generalized diagonal} move, that is a move of the form $\{pt, qt\}$, where $0 < p < q$ are fixed positive integers and $t > 0$? Does the answer perhaps depend on the specific values of $p$ and $q$? We state three conjectures of which the weakest form is: $\lim_{t\in \N}\frac{b_t}{a_t}$ exists, and equals $\Phi$, if and only if $(p, q)$ is a certain \emph{non-splitting pair}, and where $\{\{a_t, b_t\}\}$ represents the set of $P$-positions of the new game. Then we prove this conjecture for the special case $(p,q) = (1,2)$ (a \emph{splitting pair}). We prove the other direction whenever $q / p < \Phi$. In the Appendix, a variety of experimental data is included, aiming to point out some directions for future work on GDWN games.