13. Chung minh nth a la phtin tit be nhat (len nhat) cua
mot tap hop X del thi mot quan he thti td S, thi a la phein to tei lieu (t6i dal) duy nhat eim X
14. Cluing minh nth X sap Hill ttt t6t thi X sap thu toan phan.
15. Cluing minh cac tap hop trong the bid tap 10) va 11) la sap tint to tot.
§3. SO LUOC VE CAC TIEN DE CUA Li THUYET TAP HOP
1. Mb dgu
Nhu ta da ndi a. dam chuong, li thuyet tap hop ma ta da trinh bay la mat If thuyet so cap theo quan diem new this. Bay giO chting ta hay gioi thigu so Moe the tien de dia li thuyet tap hop. Ban disc mthn tim hieu ki ea the tham khao nhieu sach, ehang ban "Li thuyet tap hop" cua Bourbaki.
2. KW nidm nguyen thily
Chung ta khong Binh nghia cha tap hop : ta goi nd la khai niem nguyen thdy. Khdi niem thuec yap &toe ki higu nhu ta
da biet bang e, cling la met khai niem nguyen they.
Thy hai khai niem tap hop va thuoc vao kheng doge dinh nghia, nhung ehting to lai td an dinh the quy the : dieu gi ta ed the lam duoc va diet' gi ta khOng the lam dude vai hai khai
niem dd DO la bay tign de &la Zermelo - Fraenkel, ma chting ta them vao cal thtl tam, tien clg Chan.
Theo iruyen thong, cac ties de dd throe cho dtith ten va tint
to sau : tien de awing tinh, tien de tuyin 1ga (hay con goi tien de nOi ham, hay tien de chi re, hay tien de tach), tien de cap, tien de hop, tien de tap ling Sc b0 ph4n, tien de ue han