「単射?全射?全単射?逆写像?」【論理と集合シリーズ】写像編 まとめ② https://for-spring.com/foundation/%e3%80%8c%e5%8d%98%e5%b0%84%ef%bc%9f%e5%85%a8%e5%b0%84%ef%bc%9f%e5%85%a8%e5%8d%98%e5%b0%84%ef%bc%9f%e9%80%86%e5%86%99%e5%83%8f%ef%bc%9f%e3%80%8d%e3%80%90%e8%ab%96%e7%90%86%e3%81%a8%e9%9b%86%e5%90%88/