https://www.nikkei.com/article/DGXZQOFC017T40R00C22A6000000/
https://www.hokkaido-np.co.jp/movies/detail/6118387123001
https://www.hokkaido-np.co.jp/movies/detail/6118387134001
https://www.hokkaido-np.co.jp/movies/detail/6118388492001
https://www.nikkei.com/article/DGXMZO22309540W7A011C1L41000/
http://www.cris.hokudai.ac.jp/cris/content/files/document/cristime12%20web_4.pdf
http://www.cris.hokudai.ac.jp/cris/content/files/document/kotowari_vol2_0323_1P.pdf