beamertheorems
I'm making a poster using beamer and when I use \begin{theorem} and \begin{proof} it makes the theorems and proofs in a box just like a block title would be.
I understand this is the default setting when using beamer but I want my theorems and proofs to look like the default when just writing an article in LaTeX. Is there a way I can change the theorem style or theorem environment so that theorem and proof are no longer in boxes?
beamer provides a means to modify the start and end of a theorem environment by setting the appropriate template. The start of the theorem environment template is defined within theorem begin, and the end in the template theorem end:
\documentclass{beamer}
\makeatletter
\setbeamertemplate{theorem begin}
{%
\inserttheoremheadfont% \bfseries
\inserttheoremname \inserttheoremnumber
\ifx\inserttheoremaddition\@empty\else\ (\inserttheoremaddition)\fi%
\inserttheorempunctuation
\normalfont
}
\setbeamertemplate{theorem end}{%
% empty
}
\makeatother
\begin{document}
\begin{frame}
\begin{theorem}[Theorem name]
This is a very important theorem and requires an exceptional proof.
\end{theorem}
\end{frame}
\end{document}
\inserttheoremheadfont formats the header as \bfseries. If you want to modify this (and add some colour or perhaps even a different style (\itshape, say), input it directly as needed. Ending in \normalfont switches back to the normal font shape for typesetting the remainder of the theorem content. \inserttheoremname inserts Theorem, while \inserttheoremnumber inserts the theorem number. Whatever is specified as the optional argument to theorem is considered as a "theorem addition", and is inserted using \inserttheoremaddition. Punctuation, if any, is provided by \insertpunctuation (default is a period .).
The redefinition of theorem end is also required. In this case, it is left empty.
Update version 2.
\documentclass{scrartcl}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\newtheorem{theorem}{Theorem}[section]
\newtheorem{subtheorem}{Sub-Theorem}[theorem]
\newenvironment{proof}[1][Proof]{\begin{trivlist}
\item[\hskip \labelsep {\bfseries #1}]}{\end{trivlist}}
\newcommand{\qed}{\nobreak \ifvmode \relax \else
\ifdim\lastskip<1.5em \hskip-\lastskip
\hskip1.5em plus0em minus0.5em \fi \nobreak
\vrule height0.75em width0.5em depth0.25em\fi}
\begin{document}
\section{Introduction}
\begin{theorem}
\label{main}
If $x=2$, $x^3=8$.
\end{theorem}
\begin{proof}
Let $x=2.$
\begin{subtheorem}
\label{sub}
For all $x$ and all natural numbers $n$, $x^n = x*x*...*x$ (n times).
\end{subtheorem}
\begin{proof}
By induction. \qed
\end{proof}
(Theorem \ref{main}'s proof continued) by Claim \ref{sub}, $x^3 = 2*2*2 = 8$ .\qed
\end{proof}
\end{document}
With amsart Now I think (not sure) that your problem comes from Lyx. I think you try to use tag given in the menu but I can't give you a correct answer because I don't know Lyx.Perhaps it's possible to modify the menus, the tags etc. but I don't know ! :(
\documentclass{amsart}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\newtheorem{thm}{Theorem}[section]
\newtheorem{lem}{Lemma}[section]
\newtheorem{cor}{Corollary}[section]
\newtheorem{prop}{Proposition}[section]
\newtheorem{crit}{Criterion}[section]
\newtheorem{alg}{Algorithm}[section]
\theoremstyle{definition}
\newtheorem{defn}{Definition}[section]
\newtheorem{claim}{Claim}[thm]
\newtheorem{other}{Other}[defn]
\begin{document}
\section{Introduction}
\begin{defn}
a new definition that uses this definition
\end{defn}
\begin{thm}
\label{main}
If $x=2$, $x^3=8$.
\end{thm}
\begin{proof}
Let $x=2.$
\begin{claim}
\label{sub}
For all $x$ and all natural numbers $n$, $x^n = x*x*...*x$ (n times).
\end{claim}
\begin{proof}
By induction.
\end{proof}
(Theorem \ref{main}'s proof continued) by Claim \ref{sub}, $x^3 = 2*2*2 = 8$.
\end{proof}
\begin{defn}
a new definition that uses this definition
\begin{other}
other definition
\end{other}
\end{defn}
\end{document}
Best Answer
The style is defined by
\setbeamertemplate{theorem begin}and\setbeamertemplate{theorem end}Check page 122 of
beameruserguide.pdf. In the following I have just deleted the\inserttheoremblockenvcommands from the definition in the manual.