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\begin{align}

\Lambda=\frac{\sigma}{\sqrt{1-v^2}}

\begin{pmatrix}1 & -v\\ -\rho v & \rho\end{pmatrix}.

\end{align} Here ##\sigma=\operatorname{sgn}\Lambda_{00}## and ##\rho=\det\Lambda##. I learned today that ##\Lambda## is said to be

*orthochorous*if ##\sigma\rho=1##. I don't think I've ever heard that term before. (I found it in Streater & Wightman...which by the way is the second hit if I google the term). Can someone explain this term? Is it standard? What does the "chorous" part refer to? Now that I think about it, I realize that I don't even know what "ortho" means, so I wouldn't mind getting that explained too.

And no, I'm not misspelling "orthochronous". This is a different word.