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foo \ bar

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A test -- \begin{equation}\mu_{(i+1)} = \frac{1}{i+1} x_{(i+1)}\end{equation}.

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A test -- $\mu_{(i+1)} = \frac{1}{i+1} x_{(i+1)}$.

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A test -- $$ \mu_{(i+1)} = \frac{1}{i+1} x_{(i+1)}. $$

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A test -- \(\mu_{(i+1)} = \frac{1}{i+1} x_{(i+1)}\).

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A test -- \[\mu_{(i+1)} = \frac{1}{i+1} x_{(i+1)}\].