English

Restrictions of $m$-Wythoff Nim and $p$-complementary Beatty Sequences

Combinatorics 2010-05-25 v2

Abstract

Fix a positive integer mm. The game of \emph{mm-Wythoff Nim} (A.S. Fraenkel, 1982) is a well-known extension of \emph{Wythoff Nim}, a.k.a 'Corner the Queen'. Its set of PP-positions may be represented by a pair of increasing sequences of non-negative integers. It is well-known that these sequences are so-called \emph{complementary homogeneous} \emph{Beatty sequences}, that is they satisfy Beatty's theorem. For a positive integer pp, we generalize the solution of mm-Wythoff Nim to a pair of \emph{pp-complementary}---each positive integer occurs exactly pp times---homogeneous Beatty sequences a=(an)n\Ma = (a_n)_{n\in \M} and b=(bn)n\Mb = (b_n)_{n\in \M}, which, for all nn, satisfies bnan=mnb_n - a_n = mn. By the latter property, we show that aa and bb are unique among \emph{all} pairs of non-decreasing pp-complementary sequences. We prove that such pairs can be partitioned into pp pairs of complementary Beatty sequences. Our main results are that {{an,bn}n\M}\{\{a_n,b_n\}\mid n\in \M\} represents the solution to three new 'pp-restrictions' of mm-Wythoff Nim---of which one has a \emph{blocking maneuver} on the \emph{rook-type} options. C. Kimberling has shown that the solution of Wythoff Nim satisfies the \emph{complementary equation} xxn=yn1x_{x_n}=y_n - 1. We generalize this formula to a certain 'pp-complementary equation' satisfied by our pair aa and bb. We also show that one may obtain our new pair of sequences by three so-called \emph{Minimal EXclusive} algorithms. We conclude with an Appendix by Aviezri Fraenkel.

Keywords

Cite

@article{arxiv.0901.4683,
  title  = {Restrictions of $m$-Wythoff Nim and $p$-complementary Beatty Sequences},
  author = {Urban Larsson},
  journal= {arXiv preprint arXiv:0901.4683},
  year   = {2010}
}

Comments

22 pages, 2 figures, Games of No Chance 4, Appendix by Aviezri Fraenkel