[Tex/LaTex] \textbf inside a lemma

Question

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?

Answer 1

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}