Normal not implies direct factor
This article gives the statement and possibly, proof, of a non-implication relation between two subgroup properties. That is, it states that every subgroup satisfying the first subgroup property (i.e., normal subgroup) need not satisfy the second subgroup property (i.e., direct factor)
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Let be cyclic group of order four and be the unique subgroup of order two, comprising the squares (or the elements whose order divides two). Then:
- is a normal subgroup of .
- is not a direct factor of : In fact, it is the only proper nontrivial subgroup of .