Definition:Join of Subgroups

Definition
Let $\struct {G, \circ}$ be a group.

Let $A$ and $B$ be subgroups of $G$.

The join of $A$ and $B$ is written and defined as:
 * $A \vee B := \gen {A \cup B}$

where $\gen {A \cup B}$ is the subgroup generated by $A \cup B$.

By the definition of subgroup generator, this can alternatively be written:


 * $\displaystyle A \vee B := \bigcap \set {T: T \text { is a subgroup of } G: A \cup B \subseteq T}$

Also see

 * Join of Subgroups is Group Generated by Union where this construction is justified.


 * Union of Subgroups, where it is shown that $A \vee B = A \cup B$ iff $A \subseteq B$ or $B \subseteq A$.