# Jordan–Schur theorem

Jordan–Schur theorem In mathematics, the Jordan–Schur theorem also known as Jordan's theorem on finite linear groups is a theorem in its original form due to Camille Jordan. In that form, it states that there is a function ƒ(n) such that given a finite subgroup G of the group GL(n, C) of invertible n-by-n complex matrices, there is a subgroup H of G with the following properties: H is abelian. H is a normal subgroup of G. The index of H in G satisfies (G : H) ≤ ƒ(n).

Schur proved a more general result that applies when G is not assumed to be finite, but just periodic. Schur showed that ƒ(n) may be taken to be ((8n)1/2 + 1)2n2 − ((8n)1/2 − 1)2n2.[1] A tighter bound (for n ≥ 3) is due to Speiser, who showed that as long as G is finite, one can take ƒ(n) = n! 12n(π(n+1)+1) where π(n) is the prime-counting function.[1][2] This was subsequently improved by Hans Frederick Blichfeldt who replaced the 12 with a 6. Unpublished work on the finite case was also done by Boris Weisfeiler.[3] Subsequently, Michael Collins, using the classification of finite simple groups, showed that in the finite case, one can take ƒ(n) = (n + 1)! when n is at least 71, and gave near complete descriptions of the behavior for smaller n.

See also Burnside's problem References ^ Jump up to: a b Curtis, Charles; Reiner, Irving (1962). Representation Theory of Finite Groups and Associative Algebras. John Wiley & Sons. pp. 258–262. ^ Speiser, Andreas (1945). Die Theorie der Gruppen von endlicher Ordnung, mit Andwendungen auf algebraische Zahlen und Gleichungen sowie auf die Krystallographie, von Andreas Speiser. New York: Dover Publications. pp. 216–220. ^ Collins, Michael J. (2007). "On Jordan's theorem for complex linear groups". Journal of Group Theory. 10 (4): 411–423. doi:10.1515/JGT.2007.032. Categories: Theorems in group theory

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