Nedialkov, Evgeni, and Nedyalko Nenov. 1999. “Each 11-Vertex Graph Without 4-Cliques Has a Triangle-Free 2-Partition of Vertices”. Ann. Sofia Univ. Fac. Math. And Inf. 91 (December):127-47. https://ftl5.uni-sofia.bg./index.php/fmi/article/view/275.