... Chng 4: Lý thuyt m & Logic m CHNG : Lí THUYT TP M & LOGIC M 61 4.1 Tng quan 61 4.2 Gii thiu ... relation $ % &' Ô " #Đ Ư Ô Ê ( ! $ is an equivalence relation if and only if Proof: By denition, , for some integer Using this,we proceed: % &' Ô ) 0 Ô Â $ % &' Ô Ô Ô Ô , ... reexive 1 , and $ % $ % &' Ô Ô Đ ) Ê ) , for some integer , and we have , so Ô &' Ô , then )  If Thus, is symmetric  $ , and and $ ) 3 Ư Đ % &' , and $ Ô Therefore,...