Reconstruction and Edge Reconstruction of Triangle-free Graphs

TL;DR

This paper investigates the Reconstruction Conjecture for triangle-free graphs, proving it for certain classes with specific diameter and connectivity conditions, and extends results to the Edge Reconstruction Conjecture.

Contribution

It provides partial proofs that the Reconstruction and Edge Reconstruction Conjectures hold for triangle-free graphs with diameter 3 and those with diameter 2 and connectivity 3.

Findings

Reconstruction Conjecture holds for triangle-free graphs in 3.

Reconstruction Conjecture holds for triangle-free graphs in 2 with 3.

Similar results established for the Edge Reconstruction Conjecture.

Abstract

The Reconstruction Conjecture due to Kelly and Ulam states that every graph with at least 3 vertices is uniquely determined by its multiset of subgraphs $\{G-v: v\in V(G)\}$. Let $diam(G)$ and $\kappa(G)$ denote the diameter and the connectivity of a graph $G$, respectively, and let $\mathcal{G}_2:=\{G: \textrm{diam}(G)=2\}$ and $\mathcal{G}_3:=\{G:\textrm{diam}(G)=\textrm{diam}(\overline{G})=3\}$. It is known that the Reconstruction Conjecture is true if and only if it is true for every 2-connected graph in $\mathcal{G}_2\cup \mathcal{G}_3$. Balakumar and Monikandan showed that the Reconstruction Conjecture holds for every triangle-free graph $G$ in $\mathcal{G}_2\cup \mathcal{G}_3$ with $\kappa(G)=2$. Moreover, they asked whether the result still holds if $\kappa(G)\ge 3$. (If yes, the class of graphs critical for solving the Reconstruction Conjecture is restricted to 2-connected graphs in $\mathcal{G}_2\cup\mathcal{G}_3$ which contain triangles.) In this paper, we give a partial solution to their question by showing that the Reconstruction Conjecture holds for every triangle-free graph $G$ in $\mathcal{G}_3$ and every triangle-free graph $G$ in $\mathcal{G}_2$ with $\kappa(G)=3$. We also prove similar results about the Edge Reconstruction Conjecture.