2

I have the following issue. In my LaTeX, I use the following formats:

\newtheorem{teo}{Teorema}
\theoremstyle{plain}
\newtheorem{coro}{Corolario}
\newtheorem{defi}{Definici\'on}
\newtheorem{lema}{Lema}
\newtheorem{prop}{Proposici\'on}
\newtheorem{nota}{Nota}
\newtheorem{obs}{Observación}

So when I compile, for example:

\begin{defi}
Un semigrupo es un par $(S,\cdot)$ donde $S$ es un conjunto y $S\times S\to S$ operación asociativa, i.e. $(s_1s_2)s_3=s_1(s_2s_3)~\forall s_1,s_2,s_3\in S$.
\end{defi}
\begin{defi}
Un monoide $(M,\cdot)$ es un semigrupo con un elemento neutro $e\in M$.
\end{defi}
\begin{obs}
El neutro del monoide es único.
\end{obs}
\begin{defi}
Un grupo $G$ es un monoide con inversos: $\forall g\in G~\exists g^{-1}\in G$ tal que $gg^{-1}=g^{-1}g=e$.
\end{defi}
\begin{obs}
El inverso es único.
\end{obs}
\begin{defi}
Un grupo (o semigrupo o monoide) se dice abeliano o conmutativo si $$g_1g_2=g_2g_1~\forall g_1,g_2\in G$$.
\end{defi}

it prints enter image description here

I would like to change the font inside each definition, theorem, observation, etc. Instead of a cursive-wise or italic, I'd use a more standard one. Thank you in advance.

Fabrizio Gambelín
  • 169

1 Answers1

4

You didn't say what package you're using for defining theorems and theorem-like environments. I'm assuming you're using amsthm but there are others (like ntheorem).

The style applied to the theorem environment is determined by the most recent \theoremstyle command selected prior to the \newtheorem command for that environment.

The plain style you're using makes the text italics. There's another style, definition (appropriately enough for your use case) that does not. So select it prior to \newtheorem{defi}....

\documentclass{article}

\usepackage{amsthm}


\newtheorem{teo}{Teorema}% no theoremstyle selected, so the default (plain) is used
\theoremstyle{plain}
\newtheorem{coro}{Corolario}% uses plain style
\newtheorem{lema}{Lema}% uses plain style
\newtheorem{prop}{Proposici'on}% uses plain style
\newtheorem{nota}{Nota}% uses plain style
\newtheorem{obs}{Observación}% uses plain style


\theoremstyle{definition}
\newtheorem{defi}{Definici'on}% uses definition style


\begin{document}


\begin{defi}
Un semigrupo es un par $(S,\cdot)$ donde $S$ es un conjunto y $S\times S\to S$ operación asociativa, i.e. $(s_1s_2)s_3=s_1(s_2s_3)~\forall s_1,s_2,s_3\in S$.
\end{defi}
\begin{defi}
Un monoide $(M,\cdot)$ es un semigrupo con un elemento neutro $e\in M$.
\end{defi}
\begin{obs}
El neutro del monoide es único.
\end{obs}
\begin{defi}
Un grupo $G$ es un monoide con inversos: $\forall g\in G~\exists g^{-1}\in G$ tal que $gg^{-1}=g^{-1}g=e$.
\end{defi}
\begin{obs}
El inverso es único.
\end{obs}
\begin{defi}
Un grupo (o semigrupo o monoide) se dice abeliano o conmutativo si [g_1g_2=g_2g_1~\forall g_1,g_2\in G].
\end{defi}


\end{document}

upright definitions

If you want all of the others to work like that as well, move them to after the \theoremstyle{definition} command as well.

\theoremstyle{definition}
\newtheorem{defi}{Definici\'on}
\newtheorem{teo}{Teorema}
\newtheorem{coro}{Corolario}
\newtheorem{lema}{Lema}
\newtheorem{prop}{Proposici\'on}
\newtheorem{nota}{Nota}
\newtheorem{obs}{Observación}

It's also possible to define your own theorem styles. See the amsthm documentation for details.

(This is unrelated, but $$ ... $$ for display math is outdated for LaTeX; use \[...\] instead. See here.)

frabjous
  • 41,473