[; T(\underline{v}) = \underline{\underline{T}}~ \underline{v} ;]
[; \underline{\underline{T}} = \begin{pmatrix} 1 & 0\\ 0 & -1\\ \end{pmatrix} = \underline{\underline{S}}_{1,-1} ;]
[; \underline{\underline{T}}_1 = \begin{pmatrix} -1& 0\\ 0 & 1\\ \end{pmatrix} = \underline{\underline{S}}_{-1,1} ;]
[; \underline{\underline{T}}_{\theta} = \underline{\underline{R}}_{\theta}~ \underline{\underline{T}}~ \underline{\underline{R}}_{-\theta} = \begin{pmatrix} \cos^2{\theta}-\sin^2{\theta} & -2\cos{\theta} \sin{\theta} \\ 2\cos{\theta} \sin{\theta} & \cos^2{\theta}-\sin^2{\theta} \\ \end{pmatrix} ;]
[; \underline{\underline{T}}_{\theta}^{2n+1} = \underline{\underline{T}}_{\theta}, \quad n>1 ;]