Subgraphs with even cross-edges
Source: 2024 Israel TST Test 6 P1
March 20, 2024
combinatoricsTSTgraph theoryColoring
Problem Statement
Let be a connected (simple) graph with vertices and at least edges. Prove that it is possible to color the vertices of red and blue, so that the following conditions hold: i. There is at least one vertex of each color,
ii. There is an even number of edges connecting a red vertex to a blue vertex, and
iii. If all such edges are deleted, one is left with two connected graphs.