# Definition:Torus (Topology)

## Definition

A torus is a surface obtained by identifying both pairs of opposite sides, one with the other, of a square, while retaining the orientation:

Thus in the above diagram, $AB$ is identified with $DC$ and $CB$ with $DA$.

### General Definition

The $n$-dimensional torus (or $n$-torus) $\Bbb T^n$ is defined as the space whose points are those of the cross product of $n$ circles:

$\Bbb T^n = \underbrace{\Bbb S^1 \times \Bbb S^1 \times \ldots \times \Bbb S^1}_{n \text{ times}}$

and whose topology $\tau_{\Bbb T^n}$ is defined as:

$U \in \tau_{\Bbb T^n} \iff \exists U_1, U_2, \ldots, U_n \in \tau_{\Bbb S^1} : U = U_1 \times U_2 \times \ldots \times U_n$

where $\tau_{\Bbb S^1}$ is the topology of the circle.

## Also see

• Results about the torus can be found here.