MathDB
No two cycles share an edge

Source: ICMC 2023 Round 1 P4

November 28, 2022
college contestscombinatoricsgraph theoryICMC

Problem Statement

Let G\mathcal{G} be a simple graph with nn vertices and mm edges such that no two cycles share an edge. Prove that 2m<3n2m < 3n.
Note: A simple graph is a graph with at most one edge between any two vertices and no edges from any vertex to itself. A cycle is a sequence of distinct vertices v1,,vnv_1, \dots, v_n such that there is an edge between any two consecutive vertices, and between vnv_n and v1v_1.
Proposed by Ethan Tan