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I know one thing: that I know nothing.

I know that I know nothing.

--Socratic paradox

I know that I know nothing.

--Socratic paradox

\begin{bmatrix} 1 & 0 & \ldots & 0 \\
0 & 1 & 0 & \vdots \\
\vdots & 0 & \ddots & 0\\
0 & \ldots & 0 & 1_{n}
\end{bmatrix}