5.9.3 Graph Colourings 1. Vertex colourings Definitions 45: A proper colouring of a graph g with no loop is an assignment of colours to the vertices of G, one colour to each vertex, such that adjacent vertices receive different colours. A proper colouring in which k colours are used is a k-colouring. A graph G is k-colourable if there exists a S-colouring of G for some s<k The minimum integer k for which g is k- colourable is called the chromatic number. We denoted by X(G).If x(G=k, then g is k-chromatic5.9.3 Graph Colourings ▪ 1.Vertex colourings ▪ Definitions 45:A proper colouring of a graph G with no loop is an assignment of colours to the vertices of G, one colour to each vertex, such that adjacent vertices receive different colours. A proper colouring in which k colours are used is a k-colouring. A graph G is k-colourable if there exists a s-colouring of G for some s ≤ k. The minimum integer k for which G is k￾colourable is called the chromatic number. We denoted by (G). If (G) = k, then G is k-chromatic