Normal Subgroup
A subgroup where it is normal under conjugation: xHx^-1=H or xH=Hx
Normaliser
The set of elements that satisfy the condition of being normal under conjugation
Subgroup of index 2
Example of a NORMAL subgroup!
Quotient Group
Suppose H is a normal subgroup of a group G. Then the Quotient group is the set G/H of left cosets of H.
Quotient Map from G to G/H
Let H be a normal subgroup of a group G. The group homomorphism sending g∈G to its coset gH
Order of Quotient Group
|G|/|H|