Register to reply 
Minimal normal subgroup of a finite group. 
Share this thread: 
#1
Nov2012, 01:04 PM

P: 39

I have Theorem 1 from a research paper.
Theorem 1. Suppose that [itex]G[/itex] is a finite nonabelian simple group. Then there exists an odd prime [itex]q \in \pi(G)[/itex] such that [itex]G[/itex] has no [itex]\{2, q\}[/itex]Hall subgroup. I have Theorem 2 from a book. Theorem 2. If [itex]H[/itex] is a minimal normal subgroup of [itex]G[/itex], then either [itex]H[/itex] is an elementary abelian [itex]p[/itex]group for some prime [itex]p[/itex] or [itex]H[/itex] is the direct product of isomorphic nonabelian simple groups. I like to know if the contradicition in this argument is true. Let [itex]N[/itex] be a minimal normal subgroup of a finite group [itex]G[/itex] with [itex]2[/itex] divides the order of [itex]N[/itex] and [itex]N[/itex] is not a [itex]2[/itex]group. Let [itex]P[/itex] be a Sylow [itex]2[/itex]subgroup of [itex]N[/itex]. Suppose that for each prime [itex]q \neq 2[/itex] dividing the order of [itex]N[/itex], there exists a Sylow [itex]q[/itex]subgroup [itex]Q[/itex] of [itex]N[/itex] such that [itex]PQ[/itex] is a subgroup of [itex]N[/itex]. Cleary, [itex]N=T_{1}×T_{2}×...×T_{r}[/itex] for some postive intger [itex]r[/itex], where each [itex]T_{i}[/itex] is a nonabelian simple group. Let [itex]T[/itex] be one of the [itex]T_{i}[/itex]. It is clear that if some prime divides the order of [itex]N[/itex] then this prime must divide the order of [itex]T[/itex] as [itex]N=T^{r}[/itex]. Since [itex]T[/itex] is normal in [itex]N[/itex], then [itex]T \cap PQ=(T \cap P)(T \cap P)[/itex] (I Know that this statement is true so do not bother checking it). So, [itex]T[/itex] is a finite nonableian simple group with Hall [itex]\{2,q\}[/itex]subgroup for each odd prime dividing the order of [itex]T[/itex] which contradicts Theorem 1. Thanks in advance. 


Register to reply 
Related Discussions  
Hall subgroup of a finite group G  Linear & Abstract Algebra  0  
Is a factor group by a nontrivial normal subgroup is always smaller than the group ?  Calculus & Beyond Homework  1  
Let G be a group and H a subgroup. Prove if [G:H]=2, then H is normal.  Calculus & Beyond Homework  7  
The size of the orbits of a finite normal subgroup  Calculus & Beyond Homework  4  
Orbits of a normal subgroup of a finite group  Calculus & Beyond Homework  4 