http://www.asahi.com/business/update/0405/TKY201304050010.html

http://www.ringolab.com/note/daiya/2013/04/post-1784.html

http://gigazine.net/news/20130404-amazon-first-book/

http://japanese.donga.com/srv/service.php3?biid=2013040827018

http://www.sankeibiz.jp/econome/news/130407/ecd1304071802003-n1.htm

http://headlines.yahoo.co.jp/hl?a=20130408-00000011-mai-soci