In mathematics, the Walter theorem, proved by , describes the

finite group Finite is the opposite of infinite. It may refer to: * Finite number (disambiguation) * Finite set, a set whose cardinality (number of elements) is some natural number * Finite verb, a verb form that has a subject, usually being inflected or marked ...

s whose

Sylow 2-subgroup In mathematics, specifically in the field of finite group theory, the Sylow theorems are a collection of theorems named after the Norwegian mathematician Peter Ludwig Sylow that give detailed information about the number of subgroups of fixed ...

is abelian. used

Bender's method In group theory, Bender's method is a method introduced by for simplifying the local group theoretic analysis of the odd order theorem. Shortly afterwards he used it to simplify the Walter theorem on groups with abelian Sylow 2-subgroups , and Gor ...

to give a simpler proof.

Statement

Walter's theorem states that if ''G'' is a finite group whose 2-sylow subgroups are abelian, then ''G''/''O''(''G'') has a

normal subgroup In abstract algebra, a normal subgroup (also known as an invariant subgroup or self-conjugate subgroup) is a subgroup that is invariant under conjugation by members of the group of which it is a part. In other words, a subgroup N of the group G i ...

of odd index that is a product of groups each of which is a 2-group or one of the

simple group SIMPLE Group Limited is a conglomeration of separately run companies that each has its core area in International Consulting. The core business areas are Legal Services, Fiduciary Activities, Banking Intermediation and Corporate Service. The d ...

s PSL₂(''q'') for ''q'' = 2^''n'' or ''q'' = 3 or 5 mod 8, or the

Janko group J1 In the area of modern algebra known as group theory, the Janko group ''J1'' is a sporadic simple group of order : 233571119 = 175560 : ≈ 2. History ''J1'' is one of the 26 sporadic groups and was originally described by Zvo ...

, or

Ree group In mathematics, a Ree group is a group of Lie type over a finite field constructed by from an exceptional automorphism of a Dynkin diagram that reverses the direction of the multiple bonds, generalizing the Suzuki groups found by Suzuki using a dif ...

s ²''G''₂(3^2''n''+1). (Here ''O(G)'' denotes the unique largest normal subgroup of ''G'' of odd order.) The original statement of Walter's theorem did not quite identify the Ree groups, but only stated that the corresponding groups have a similar subgroup structure as Ree groups. and later showed that they are all Ree groups, and gave a unified exposition of this result.

References

* * * * * * * *{{Citation , last1=Walter , first1=John H., authorlink=John H. Walter , title=The characterization of finite groups with abelian Sylow 2-subgroups. , jstor=1970648 , mr=0249504 , year=1969 , journal=

Annals of Mathematics The ''Annals of Mathematics'' is a mathematical journal published every two months by Princeton University and the Institute for Advanced Study. History The journal was established as ''The Analyst'' in 1874 and with Joel E. Hendricks as the ...

, series=Second Series , issn=0003-486X , volume=89 , pages=405–514 , doi=10.2307/1970648 Theorems about finite groups