... gi'eng cua nhau.2. PHI vaQkla 4-lang gieng cii a nhau.3.QjvaQkla 8-lang gieng ciia nhau.4. Cac di~mPila vung thiQj, Qkla nen va ngtro'c lai.Djnh nghia 2.3. [Chu tuyen ngoai]Chu ... G9i x EXvaBEH(X),khi d6 khoang each tu: diimxt61. t~pBdircc dinh nghia la:d(x, B)=min{d(x,y) :yEB}.D!nhnghia3.2.[Khoing each giira2t~p ho'p](X,d) la khOng gian metric ... day du, A, BEH(X),khi d6 khoang eachtitt~p A t&i t~p B dirccdinh nghia boi:d(A,B)=max{d(x,B) : xEA}.D!nhnghia 3.3.[Khoang each Hausdorff](X,d) la khOng gian metric day duo Khoang...