Lagrange's theorem in group theory

E156184

Lagrange's theorem in group theory is a fundamental result stating that the order of any subgroup of a finite group divides the order of the group.

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Lagrange's theorem in group theory canonical 1

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Predicate Object
instanceOf result in abstract algebra
theorem in group theory
appliesTo finite groups
assumes group is finite
category finite group theory
definesConcept index of a subgroup
doesNotGenerallyHoldFor infinite groups
exampleApplication in a group of order 12, any subgroup has order dividing 12
in a group of prime order p, every non-identity element generates the group
field group theory
generalizationOf divisibility of orders in cyclic groups
hasConsequence the index of a subgroup divides the order of the group
historicalPeriod 18th century mathematics
holdsIn finite abelian groups
finite non-abelian groups
implies the order of a subgroup equals the number of its left cosets times the order of the subgroup
the order of any element of a finite group divides the order of the group
|G| = [G : H] · |H| for finite group G and subgroup H
importance fundamental theorem for structure of finite groups
isGeneralizedBy Cauchy's theorem in group theory
Sylow theorems
isRelatedTo Burnside's lemma
Cayley's theorem
orbit-stabilizer theorem
mathematicalDomain algebra
discrete mathematics
namedAfter Joseph-Louis Lagrange
proofMethod partition of the group into left cosets of a subgroup
relatesConcept group order
subgroup order
requiresPrerequisite definition of coset
definition of group
definition of group order
definition of subgroup
statement For a finite group G and a subgroup H of G, the order of H divides the order of G
typicalNotation [G : H] for index of H in G
|G| for order of group G
|H| for order of subgroup H
usedFor classifying small finite groups
proving that groups of prime order are cyclic
showing that certain subgroups cannot exist in a given finite group
usedIn element order computations
finite group actions
proving non-existence of elements of certain orders
usesConcept equivalence relation induced by a subgroup
left coset
right coset

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Joseph-Louis Lagrange knownFor Lagrange's theorem in group theory