{ localUrl: '../page/normal_subgroup.html', arbitalUrl: 'https://arbital.com/p/normal_subgroup', rawJsonUrl: '../raw/4h6.json', likeableId: '2826', likeableType: 'page', myLikeValue: '0', likeCount: '1', dislikeCount: '0', likeScore: '1', individualLikes: [ 'EricBruylant' ], pageId: 'normal_subgroup', edit: '5', editSummary: '', prevEdit: '4', currentEdit: '5', wasPublished: 'true', type: 'wiki', title: 'Normal subgroup', clickbait: 'Normal subgroups are subgroups which are in some sense "the same from all points of view".', textLength: '747', alias: 'normal_subgroup', externalUrl: '', sortChildrenBy: 'likes', hasVote: 'false', voteType: '', votesAnonymous: 'false', editCreatorId: 'PatrickStevens', editCreatedAt: '2016-06-18 15:43:43', pageCreatorId: 'PatrickStevens', pageCreatedAt: '2016-06-17 10:27:44', seeDomainId: '0', editDomainId: 'AlexeiAndreev', submitToDomainId: '0', isAutosave: 'false', isSnapshot: 'false', isLiveEdit: 'true', isMinorEdit: 'false', indirectTeacher: 'false', todoCount: '1', isEditorComment: 'false', isApprovedComment: 'true', isResolved: 'false', snapshotText: '', anchorContext: '', anchorText: '', anchorOffset: '0', mergedInto: '', isDeleted: 'false', viewCount: '50', text: 'A *normal subgroup* $N$ of group $G$ is one which is closed under [4gk conjugation]: for all $h \\in G$, it is the case that $\\{ h n h^{-1} : n \\in N \\} = N$.\nIn shorter form, $hNh^{-1} = N$.\n\nSince [4gk conjugacy is equivalent to "changing the worldview"], a normal subgroup is one which "looks the same from the point of view of every element of $G$".\n\nA subgroup of $G$ is normal if and only if it is the [49y kernel] of some [-47t] from $G$ to some group $H$. 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