Block-avoiding point sequencings of Mendelsohn triple systems

Donald L. Kreher, Douglas R. Stinson, Shannon Veitch

Published 2019-09-19Version 1

A cyclic ordering of the points in a Mendelsohn triple system of order $v$ (or MTS$(v)$) is called a sequencing. A sequencing $D$ is $\ell$-good if there does not exist a triple $(x,y,z)$ in the MTS$(v)$ such that (1) the three points $x,y,$ and $z$ occur (cyclically) in that order in $D$; and (2) $\{x,y,z\}$ is a subset of $\ell$ cyclically consecutive points of $D$. In this paper, we prove some upper bounds on $\ell$ for MTS$(v)$ having $\ell$-good sequencings and we prove that any MTS$(v)$ with $v \geq 7$ has a $3$-good sequencing. We also determine the optimal sequencings of every MTS$(v)$ with $v \leq 10$.