of a group G that possesses a subgroup H. A coset of G modulo H determined by the element x of G is a subset:
where ° is the dyadic operation defined on
G. A subset of the former kind is called a
left coset of
G modulo
H or a left coset of
G in
H; the latter is a
right coset. In special cases
for any
x in
G. Then
H is called a
normal subgroup of
G. Any subgroup of an abelian group is a normal subgroup.
The cosets of G in H form a partition of the group G, each coset showing the same number of elements as H itself. These can be viewed as the equivalence classes of a left coset relation defined on the elements g1 and g2 of G as follows:
Similarly a
right coset relation can be defined. When
H is a normal subgroup the coset relation becomes a congruence relation.
Cosets have important applications in computer science, e.g. in the development of efficient codes needed in the transmission of information and in the design of fast adders.