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  2. Rank of a group - Wikipedia

    en.wikipedia.org/wiki/Rank_of_a_group

    Indeed, for p-groups, the rank of the group P is the dimension of the vector space P/Φ(P), where Φ(P) is the Frattini subgroup. The rank of a group is also often defined in such a way as to ensure subgroups have rank less than or equal to the whole group, which is automatically the case for dimensions of vector spaces, but not for groups such ...

  3. Nilpotent group - Wikipedia

    en.wikipedia.org/wiki/Nilpotent_group

    If a group has nilpotency class at most n, then it is sometimes called a nil-n group. It follows immediately from any of the above forms of the definition of nilpotency, that the trivial group is the unique group of nilpotency class 0, and groups of nilpotency class 1 are exactly the non-trivial abelian groups. [2] [3]

  4. Simple group - Wikipedia

    en.wikipedia.org/wiki/Simple_group

    Similarly, the additive group of the integers (, +) is not simple; the set of even integers is a non-trivial proper normal subgroup. [1] One may use the same kind of reasoning for any abelian group, to deduce that the only simple abelian groups are the cyclic groups of prime order. The classification of nonabelian simple groups is far less trivial.

  5. Group cohomology - Wikipedia

    en.wikipedia.org/wiki/Group_cohomology

    This is in fact the significance in group-theoretical terms of the unique non-trivial element of (/,),. An example of a second cohomology group is the Brauer group: it is the cohomology of the absolute Galois group of a field k which acts on the invertible elements in a separable closure:

  6. p-group - Wikipedia

    en.wikipedia.org/wiki/P-group

    In mathematics, specifically group theory, given a prime number p, a p-group is a group in which the order of every element is a power of p.That is, for each element g of a p-group G, there exists a nonnegative integer n such that the product of p n copies of g, and not fewer, is equal to the identity element.

  7. Extra special group - Wikipedia

    en.wikipedia.org/wiki/Extra_special_group

    A p-group G is called extraspecial if its center Z is cyclic of order p, and the quotient G/Z is a non-trivial elementary abelian p-group. Extraspecial groups of order p 1+2n are often denoted by the symbol p 1+2n. For example, 2 1+24 stands for an extraspecial group of order 2 25.

  8. Torsion-free abelian group - Wikipedia

    en.wikipedia.org/wiki/Torsion-free_abelian_group

    A non-finitely generated countable example is given by the additive group of the polynomial ring [] (the free abelian group of countable rank). More complicated examples are the additive group of the rational field Q {\displaystyle \mathbb {Q} } , or its subgroups such as Z [ p − 1 ] {\displaystyle \mathbb {Z} [p^{-1}]} (rational numbers ...

  9. Direct sum of groups - Wikipedia

    en.wikipedia.org/wiki/Direct_sum_of_groups

    The group operation in the external direct sum is pointwise multiplication, as in the usual direct product. This subset does indeed form a group, and for a finite set of groups {H i} the external direct sum is equal to the direct product. If G = ΣH i, then G is isomorphic to Σ E {H i}. Thus, in a sense, the direct sum is an "internal ...