3x3 tensor matrix structure.
Rendering
\usepackage{tensormatrix}
$\begin{tmat}{3}{3} \tmatpv{1}{1} \tmatpv{2}{2} \tmatpv{3}{3} \tmatlink{1 1}{2 2} \end{tmat}$
braids
Simple Crossing
tensormatrix
Metric Tensor