http://akademeia.info/index.php?%B7%D7%BB%BB%CE%CC http://edu.inf.shizuoka.ac.jp/lecture/2010/X151/text/complexity.html http://wikiwiki.jp/kut-pg/?%A5%A2%A5%EB%A5%B4%A5%EA%A5%BA%A5%E0%CA%D9%B6%AF%B2%F1%2F%B7%D7%BB%BB%CE%CC