Every finite non-solvable group has a minimal simple group as subquotient
Statement
Suppose is a finite group that is not solvable. Then, there exists a Minimal simple group (?) arising as a subquotient of .
Facts used
- Subquotient is transitive: A subquotient of a subquotient is a subquotient.
Proof
Given: A finite non-solvable group .
To prove: There exists a minimal simple group arising as a subquotient of .
Proof: We prove this by induction on the order of . We assume that the result has been proved for all groups of order strictly less than the order of . We make three cases:
- is itself a minimal simple group -- it is simple non-Abelian and every proper subgroup is solvable: In this case, is itself the desired subquotient.
- is not simple: Since is not solvable by assumption, must have a composition factor that is a simple non-Abelian group. Since any composition factor is a subquotient, has a subquotient of smaller size that is also not solvable. By induction, this subquotient has a minimal simple group as subquotient, so by fact (1), has a minimal simple subquotient.
- is simple but not minimal simple: Since is not solvable, must be a simple non-Abelian group. Since it is not minimal simple by assumption, there is some subgroup of that is not solvable. By the inductive assumption, this subgroup has a minimal simple subquotient, so by fact (1), has a minimal simple subquotient.