2Kermack W O, Mckendrick A G . A Contribution to the Mathematical Theory of Epidemics [ J ] . Royal Society of London Proceedings, 1927, 115 (772) :700-721.
3Sudbury A . The Proportion of the Population Never Hearing a Rumour [ J ]. Journal of Applied Probability, 1985, 22 ( 2 ): 443-446.
