On the BCI Problem

TL;DR

This paper investigates the BCI problem for Haar graphs, providing a theoretical framework for isomorphism testing, especially for abelian groups, and offers solutions for specific cases like cyclic groups of odd order.

Contribution

It generalizes the BCI problem, develops a theoretical approach for isomorphism testing, and solves the problem for certain classes of abelian and cyclic groups.

Findings

A theoretical method for the generalized BCI problem.

Reduction of the problem to related quotient or Cayley digraphs.

Solution of the isomorphism problem for cyclic groups of odd order.

Abstract

Let $G$ be a group. The BCI problem asks whether two Haar graphs of $G$ are isomorphic if and only if they are isomorphic by an element of an explicit list of isomorphisms. We first generalize this problem in a natural way and give a theoretical way to solve the isomorphism problem for the natural generalization. We then restrict our attention to abelian groups and, with an exception, reduce the problem to the isomorphism problem for a related quotient, component, or corresponding Cayley digraph. For Haar graphs of an abelian group of odd order with connection sets $S$ those of Cayley graphs (i.e. $S = -S$), the exception does not exist. For Haar graphs of cyclic groups of odd order with connection sets those of a Cayley graph, among others, we solve the isomorphism problem.