homomorphisms of simple groups
If a group is simple, and is an arbitrary group then anyhomomorphism of to must either map all elements of to theidentity
of or be one-to-one.
The kernel of a homomorphism must be a normal subgroup. Since issimple, there are only two possibilities: either the kernel is all of of it consists of the identity. In the former case, thehomomorphism will map all elements of to the identity. In thelatter case, we note that a group homomorphism is injective iff the kernelis trivial.
This is important in the context of representation theory. In thatcase, is a linear group and this result may be restated as sayingthat representations of a simple group are either trivial or faithful.