Erfang, Shan, Liying, Kang, and Qin, Lu. “K-Semikernels, K-Quasikernels, K-Kernels in Digraphs and Their Line Digraphs”. Utilitas Mathematica 72 (May 9, 2007). Accessed May 8, 2026. https://utilitasmathematica.com/index.php/Index/article/view/502.