## SelfAntiCommuting

Make components of tensors anti-commute.

Used to make objects with indices anti-commuting when their index
values are different. Example:\psi^{\mu}::SelfAntiCommuting.
ex:= \psi^{\nu} \psi^{\mu};

\(\displaystyle{}\psi^{\nu} \psi^{\mu}\)

canonicalise(_);

\(\displaystyle{}-\psi^{\mu} \psi^{\nu}\)

ex:= \psi^{\mu} \psi^{\mu};

\(\displaystyle{}\psi^{\mu} \psi^{\mu}\)

canonicalise(_);

\(\displaystyle{}0\)

This could not be handled with

`AntiCommuting`

because that
property handles the behaviour of \emph{different} expression patterns.