https://www.google.co.jp/url?sa=t&source=web&rct=j&url=http://mail.lib.hit-u.ac.jp/rs/bitstream/10086/14402/1/pie_dp60.pdf&ved=2ahUKEwi37IXB68XhAhXMTbwKHbyhC_YQFjABegQIBxAB&usg=AOvVaw0P1gZl31osr6J23vS7QFfF&cshid=1554911869883
https://www.google.co.jp/url?sa=t&source=web&rct=j&url=http://mail.lib.hit-u.ac.jp/rs/bitstream/10086/14402/1/pie_dp60.pdf&ved=2ahUKEwi37IXB68XhAhXMTbwKHbyhC_YQFjABegQIBxAB&usg=AOvVaw0P1gZl31osr6J23vS7QFfF&cshid=1554911869883