English

A conjecture on the Crazy Knight's Tour Problem

Combinatorics 2026-05-05 v2

Abstract

Let AA be an m×nm\times n toroidal array containing filled and empty cells. Fix an orientation R=(r1,,rm)R=(r_1,\dots,r_m) of each row and an orientation C=(c1,,cn)C=(c_1,\dots,c_n) of each column of AA. Given an initial filled cell (i1,j1)(i_1,j_1) consider the list LR,C=((i1,j1),(i2,j2),,(ik,jk), L_{R,C}=((i_1,j_1),(i_2,j_2),\ldots,(i_k,j_k), (ik+1,jk+1),)(i_{k+1},j_{k+1}),\ldots) where jk+1j_{k+1} is the column index of the filled cell (ik,jk+1)(i_k,j_{k+1}) of the row RikR_{i_k} next to (ik,jk)(i_k,j_k) in the orientation rikr_{i_k}, and where ik+1i_{k+1} is the row index of the filled cell of the column Cjk+1C_{j_{k+1}} next to (ik,jk+1)(i_k,j_{k+1}) in the orientation cjk+1c_{j_{k+1}}. The problem is the following. Crazy Knight's Tour Problem: Do there exist RR and CC such that the list LR,CL_{R,C} covers all the filled cells of AA? This problem was introduced by Costa, Dalai and Pasotti to construct new biembeddings of graphs on surfaces starting from an Heffter array. Here we provide solution to the Crazy Knight's Tour Problem for infinite classes of cyclically kk-diagonal square arrays, namely square arrays whose filled cells are exactly those of kk consecutive diagonals. These new constructions together with some known results induce us to propose the following. Conjecture: Let AA be a cyclically kk-diagonal square array of order nn. Then there exists a solution to the Crazy Knight's Tour Problem on AA if and only if nn and kk are odd integers with nk3n\geq k \geq3.

Cite

@article{arxiv.2311.09054,
  title  = {A conjecture on the Crazy Knight's Tour Problem},
  author = {Lorenzo Mella and Anita Pasotti},
  journal= {arXiv preprint arXiv:2311.09054},
  year   = {2026}
}
R2 v1 2026-06-28T13:22:13.218Z