# Quotient of UT(3,Q) by a central Z

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## Definition

The group described here is a quotient group of unitriangular matrix group:UT(3,Q) by a central subgroup isomorphic to the group of integers, which we can think of as a Z in Q inside the center, which is a copy of $\mathbb{Q}$. Explicitly, it is matrices of the form:

$\{ \begin{pmatrix} 1 & a_{12} & \overline{a_{13}} \\ 0 & 1 & a_{23} \\ 0 & 0 & 1 \\\end{pmatrix} \mid a_{12},a_{23} \in \mathbb{Q}, \overline{a_{13}} \in \mathbb{Q}/\mathbb{Z} \}$

with the matrix multiplication defined as:

$\begin{pmatrix} 1 & a_{12} & \overline{a_{13}} \\ 0 & 1 & a_{23} \\ 0 & 0 & 1 \\\end{pmatrix}\begin{pmatrix} 1 & b_{12} & \overline{b_{13}} \\ 0 & 1 & b_{23} \\ 0 & 0 & 1 \\\end{pmatrix} = \begin{pmatrix} 1 & a_{12} + b_{12} & \overline{a_{12}b_{23}} + \overline{a_{13}} + \overline{b_{13}} \\ 0 & 1 & a_{23} + b_{23} \\ 0 & 0 & 1 \\\end{pmatrix}$

where $\overline{a_{12}b_{23}}$ is understood to be the image of $a_{12}b_{23}$ under the quotient map $\mathbb{Q} \to \mathbb{Q}/\mathbb{Z}$.

## Arithmetic functions

Function Value Similar groups Explanation
order countably infinite
exponent infinite (elements of infinite order)
nilpotency class 2
derived length 2

## Group properties

Property Meaning Satisfied? Explanation Comment
abelian group any two elements commute No
group of nilpotency class two Yes
metabelian group Yes
torsion-free group No