Sylow normal-subgroup applications
For distinct primes p<q, a group of order pq has one Sylow q-subgroup, so it is normal.
Key knowledge
For distinct primes p<q, a group of order pq has one Sylow q-subgroup, so it is normal. If q≢1 mod p, its Sylow p-subgroup is also unique, and the group is cyclic. These follow by intersecting the count divisors with nₚ≡1 mod p, not by treating Lagrange's converse as true.
Conditions and scope
- The cyclic conclusion uses the additional congruence restriction.
- Failure of a uniqueness test does not itself prove that a subgroup is nonnormal.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Theorem 14.10 and proof, with Example 14.11 order15; direct-product/commutation implications retained.
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Entry details
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- math-sylow-normal-subgroup-test
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- university-core.1
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- University core expansion