1Cento,A.The Airline Industry. Challenges in the 21st Cen- tury [M],Heidelberg,2009.
2Forbes,SJ and Lederman, Mara. The Role of Regiona Airlines in the U.S.Airline In- dustry [A],in: Darin Lee (ed.),Adv&nces in Airline Economics [C],Vo. ,Esever 2007.
3L&nc&ster, Kelvin. Variety, Equity, &nd Efficiency:product v&riety in &n industri&l society [M],New York, NY : Columbi& University Press, 1979.