Another way to put this is saying that right and left cosets of N in G coincide:
Normal subgroups are of relevance because if N is normal, then the factor group G/N may be formed. Normal subgroups of G are precisely the kernels of group homomorphisms f : G > H.
{e} and G are always normal subgroups of G. If these are the only ones, then G is said to be simple.
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