Ans :
Definition: A k-edge colouring of a graph G is an assignment of k colours to the
edges of G in such a way that no two edges incident with the same vertex have the
same colour. A graph is k-edge colourable if it has a k-edge colouring. The
minimum number of colours required to colour the edges of a graph is called the edge
chromatic number of G, usually denoted by χ'(G).
