http://www.atmarkit.co.jp/bbs/phpBB/viewtopic.php?topic=8950&forum=7

http://akademeia.info/main/math_lecture.htm

つ http://blog.drecom.jp/lucky-garden/archive/39 と つ http://blog.drecom.jp/lucky-garden/archive/38

http://www.lego.com/eng/factory/design/ldd.asp