[1] Common Lispと時間とタイムゾーン - octahedron () http://octahedron.hatenablog.jp/entry/2018/12/04/000031
[2] Universal time と協定世界時(UTC) : セマンティックウェブ・ダイアリー () http://blog.livedoor.jp/s-koide/archives/2268050.html
[3] LOCAL-TIME :: A Common Lisp Library for Times and Dates () https://common-lisp.net/project/local-time/
[4] Erik Naggum — A Long, Painful History of Time (Erik Naggum著, ) http://naggum.no/lugm-time.html