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Subgroup

From Online Dictionary of Crystallography

Revision as of 15:29, 10 October 2017 by MassimoNespolo (talk | contribs) (two languages added)

زمرة جزئية (Ar); Sous-groupe (Fr); Untergruppe (Ge); Sottogruppo (It); 部分群 (Ja); Подгруппа (Ru); Subgrupo (Sp).


Let G be a group and H a non-empty subset of G. Then H is called a subgroup of G if the elements of H obey the group postulates, i.e. if

  1. the identity element 1G of G is contained in H;
  2. H is closed under the group operation (inherited from G);
  3. H is closed under taking inverses.

The subgroup H is called a proper subgroup of G if there are elements of G not contained in H.

A subgroup H of G is called a maximal subgroup of G if there is no proper subgroup M of G such that H is a proper subgroup of M.

See also