http://ru.wikipedia.org/wiki/%D0%A1%D0%B5%D0%BA%D1%81%D1%83%D0%B0%D0%BB%D1%8C%D0%BD%D1%8B%D0%B9_%D1%84%D0%B5%D1%82%D0%B8%D1%88%D0%B8%D0%B7%D0%BC#.D0.A4.D0.B5.D1.82.D0.B8.D1.88.D0.B8читай