Completely regular codes in the infinite hexagonal grid

Sergey V. Avgustinovich, Denis S. Krotov, Anastasia Yu. Vasil'eva

A set $C$ of vertices of a simple graph is called a completely regular code if for each $i=0$, $1$, $2$, \ldots and $j=i-1$, $i$, $i+1$, all vertices at distance $i$ from $C$ hav…