http://flogiston.ru/library/piazhe1
http://ru.wikipedia.org/wiki/%D0%97%D0%B0%D0%BA%D0%BE%D0%BD_%D0%95%D1%80%D0%BA%D1%81%D0%B0-%D0%94%D0%BE%D0%B4%D1%81%D0%BE%D0%BD%D0%B0
http://wiki.myword.ru/index.php/%D0%97%D0%B0%D0%BA%D0%BE%D0%BD_%D0%99%D0%B5%D1%80%D0%BA%D1%81%D0%B0-%D0%94%D0%BE%D0%B4%D1%81%D0%BE%D0%BD%D0%B0