normal subgroup
subgroup invariant under conjugation
ProofWiki: Definition:Normal_SubgroupMathWorld: NormalSubgroup
Encyclopedia of Mathematics: Normal_subgroup
Wikipedia (English): Normal_subgroup
Wikidata: normal subgroup
nLab: normal subgroup
mathswitch — infrastructure for relaying and exchanging mathematical concepts
subgroup invariant under conjugation
ProofWiki: Definition:Normal_Subgroup