6.4.2 Coset Let H;* is a subgroup of the group IG;*. We define a relation R on G, So that arb iff for a*b1∈ H for va,b∈G.The relation is called congruence relation on the subgroup H; *. We denoted by a=b(modH)。 Theorem 6.18: Congruence relation on the subgroup H; of the group G is an equivalence relation6.4.2 Coset Let [H;] is a subgroup of the group [G;]. We define a relation R on G, so that aRb iff for ab -1H for a,bG. The relation is called congruence relation on the subgroup [H;]. We denoted by ab(mod H)。 Theorem 6.18 ：Congruence relation on the subgroup [H;] of the group G is an equivalence relation