On the number of quasi-kernels in digraphs.

Gregory Gutin Khee Meng Koh Eng Guan Tay Anders Yeo On the number of quasi-kernels in digraphs. 48-56 2004 46 Journal of Graph Theory 1 http://dx.doi.org/10.1002/jgt.10169 db/journals/jgt/jgt46.html#GutinKTY04