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In mathematics, the lattice of subgroups of a group is the lattice whose elements are the subgroups of , with the partial ordering being set inclusion. In this lattice, the join of two subgroups is the subgroup generated by their union , and the meet of two subgroups is their intersection .
One of the non-abelian groups is the semidirect product of a normal cyclic subgroup of order p 2 by a cyclic group of order p. The other is the quaternion group for p = 2 and a group of exponent p for p > 2. Order p 4: The classification is complicated, and gets much harder as the exponent of p increases.
In mathematics, especially in the area of algebra known as group theory, the term Z-group refers to a number of distinct types of groups: in the study of finite groups, a Z-group is a finite group whose Sylow subgroups are all cyclic. in the study of infinite groups, a Z-group is a group which possesses a very general form of central series.
The subgroup test provides a necessary and sufficient condition for a nonempty subset of a group to be a subgroup: it is sufficient to check that for all elements and in . Knowing a group's subgroups is important in understanding the group as a whole.
A proper subgroup of a group G is a subgroup H which is a proper subset of G (that is, H ≠ G). This is often represented notationally by H < G, read as "H is a proper subgroup of G". Some authors also exclude the trivial group from being proper (that is, H ≠ {e} ). [2] [3] If H is a subgroup of G, then G is sometimes called an overgroup of H.
An algebraic subgroup of an algebraic group is a subvariety of that is also a subgroup of (that is, the maps and defining the group structure map and , respectively, into ). A morphism between two algebraic groups G , G ′ {\displaystyle \mathrm {G} ,\mathrm {G} '} is a regular map G → G ′ {\displaystyle \mathrm {G} \to \mathrm {G} '} that ...
It is possible to define a graph with vertices and edges the disjoint union of all coset spaces Γ/G x and Γ/G y respectively. This graph is a tree, called the universal covering tree, on which Γ acts. It admits the graph Y as fundamental domain. The graph of groups given by the stabilizer subgroups on the fundamental domain corresponds to ...
The principal congruence subgroup of level 2, Γ(2), is also called the modular group Λ. Since PSL(2, Z/2Z) is isomorphic to S 3, Λ is a subgroup of index 6. The group Λ consists of all modular transformations for which a and d are odd and b and c are even.