Definition (Dedekind-infinite Dedekind-finite (Dedekind,1888)) A set A is Dedekind-infinite if there is a bijective function from A onto some proper subset B of A. A set is Dedekind-finite if it is not Dedekind-infinite. another way This is a theorem in our theory of infinity. Hengfeng Wei (hfweixinju.edu.cn) 1-11 Set Theory (IV):Infinity 2019年12月17日11/49Definition (Dedekind-infinite & Dedekind-finite (Dedekind, 1888)) A set A is Dedekind-infinite if there is a bijective function from A onto some proper subset B of A. A set is Dedekind-finite if it is not Dedekind-infinite. This is a theorem in our theory of infinity. Hengfeng Wei (hfwei@nju.edu.cn) 1-11 Set Theory (IV): Infinity 2019 年 12 月 17 日 11 / 49