>>200
http://www.kurims.kyoto-u.ac.jp/~kyodo/kokyuroku/contents/pdf/1259-5.pdf
http://kazuschool.blog94.fc2.com/blog-entry-58.html
http://www.ravco.jp/cat/view.php?cat_id=6067&PHPSESSID=tfo9qitjod75rojcrt7gmred52
http://www.ne.jp/asahi/search-center/internationalrelation/mathWeb/arithmetic/AbsoluteValue/AbsThrm8Prf.htm
http://ziddy.japan.zdnet.com/qa3760839.html