# \textbf inside a lemma

I have defined lemma and use it as follows:

\newtheorem{theorem}{Theorem}[section]
\newtheorem{lemma}[theorem]{Lemma}
...
\begin{lemma}
abc_\textbf{indice}
\end{lemma}


It turns out that the indice becomes italic, does anyone know how to just make it bold, not italic?

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You can use the underscore in such contents only in math mode. –  Marco Daniel Dec 24 '11 at 15:18
By default LaTeX typesets the contents of a theorem created via \newtheorem using \itshape, or italics. –  Werner Dec 24 '11 at 16:02

It won't look pretty, but you may switch off italics inside the Lemma by using \textup{\textbf{indice}}.

\documentclass{article}

\newtheorem{lemma}{Lemma}

\begin{document}

\begin{lemma}
$$abc_\textup{\textbf{indice}}$$
\end{lemma}

\end{document}


EDIT: As egreg has commented, \mathbf may be a better choice.

\documentclass{article}

\newtheorem{lemma}{Lemma}

\begin{document}

\begin{lemma}
$$abc_\mathbf{indice}$$
\end{lemma}

\end{document}


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It would be better \mathbf, perhaps. Commands such as \textbf work correctly in subscripts only if amsmath is loaded, though. –  egreg Dec 24 '11 at 15:09