# \emph in math mode

I am new to LaTeX and have a problem with the line

The difference is that the signing key \emph{x} is split into two pieces, \begin{math}
\emph{x_{L}}\end{math} and \begin{math}\emph{x_{R}}\end{math} and are both elements of the
\begin{math}\textbf{Z}_{q}\end{math}.


I get the error

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