Popis: |
A clique of a graph G is a complete subgraph maximal under inclusion and having at least two vertices. A clique-transversal set D of a graph G is a set of vertices of G such that D meets all cliques of G . The clique-transversal number, denoted by ? c ( G ) , is the cardinality of a minimum clique-transversal set in G . Wang et?al. (2014) proved that ? c ( G ) = ? n 3 ? for any 2-connected { K 1 , 3 , K 4 } -free 4-regular graph of order n , and conjectured that ? c ( G ) ? 10 n + 3 27 for a connected { K 1 , 3 , K 4 } -free 4-regular graph of order n .In this paper, we give a short proof of the aforementioned theorem of Wang et?al. and show that the above conjecture is true, apart from only three exceptions. |