# How to remove parentheses when I refer to some lemma or proposition

I have the following TeX document:

\documentclass[12pt,a4paper]{article}
\usepackage[left=19mm,right=19mm,top=20mm,bottom=22mm]{geometry}
\usepackage{makeidx, graphicx, amsmath, amsthm, amssymb, ae}
\setcounter{MaxMatrixCols}{20}
\setlength{\textheight}{260mm}
\setlength{\textwidth}{170mm}
\usepackage[T1]{fontenc}

\newtheoremstyle{italiktekst} %name
{5mm}    %Space above, empty = usual value'
{0mm}    %Space below
{\itshape}   %Body font
{}           %Indent amount (empty = no indent, \parindent = para indent)
{\newline}   %Space after thm head: \newline = linebreak

\theoremstyle{italiktekst}
\swapnumbers
\newtheorem{theorem}{Theorem}[section]
\newtheorem{lemma}[theorem]{Lemma}
\newtheorem{corollary}[theorem]{Corollary}
\newtheorem{proposition}[theorem]{Proposition}
\newtheorem{problem}[theorem]{Problem}

\renewcommand{\thesection}{\arabic{section}.}
\renewcommand{\thetheorem}{(\thesection\arabic{theorem})}

\setcounter{page}{5}
\begin{document}
\setcounter{section}{-1}
\raggedright

\section{\rm Perron-Frobenius theorem}

\begin{lemma}
\hspace*{5mm}
\label{U_Ainvariant_UT_Ainvariant}
Let $\langle \cdot, \cdot\rangle$ be the standard inner product for ...
\end{lemma}

\vspace*{5mm}
\textbf{\textit{Proof:}}
Recall that for a subspace $\mathcal{U}$ is said to be ...
\hfill{$\square$}\\

\begin{lemma}
\hspace*{5mm}
\label{columns_independent_AP_PD}
Consider arbitrary rectangular matrix $P$ of order
$m\times n$ in which columns are linearly independent.
The column space ...
\end{lemma}

\vspace*{5mm}
\textbf{\textit{Proof:}} Denote by $\mathcal{M}$ column
space ...
\hfill{$\square$}\\

...

\vspace*{5mm}
Recall that, from Lemma \ref{U_Ainvariant_UT_Ainvariant} we have...

\vspace*{5mm}...in Lemma \ref{columns_independent_AP_PD} we have shown that...

\end{document}


Result for this code is following:

What bothers me is how to remove the parentheses when I refer to some lemma or proposition (see picture below)

Does anyone have any idea?

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Welcome to TeX.sx! –  Peter Jansson Mar 7 '13 at 22:04

I changed your style definition to

\newtheoremstyle{italiktekst} %name
{5mm}    %Space above, empty = usual value'
{5mm}    %Space below
{\itshape}   %Body font
{}           %Indent amount (empty = no indent, \parindent = para indent)
{\newline}   %Space after thm head: \newline = linebreak


i.e., specified the theorem head with the number in parentheses, removed the parentheses from the theorem counter, i.e.,

\renewcommand{\thetheorem}{\thesection\arabic{theorem}}


and finally removed \swapnumbers to obtain:

Note that I also added a 5mm skip below the theorem, as you do this by hand after both lemmata. To typeset the proofs I recommend the proof environment from amsthm, it will automatically set a q.e.d. symbol for you, by default the empty square. To make the word Proof also bold, followed by a :, I changed the default definition slightly:

\makeatletter
\renewenvironment{proof}[1][\proofname]{\par
\pushQED{\qed}%
\normalfont \topsep6\p@\@plus6\p@\relax
\trivlist
\item[\hskip\labelsep
\bfseries\itshape
}{%
\popQED\endtrivlist\@endpefalse
}
\makeatother


Complete example:

\documentclass[12pt,a4paper]{article}
\usepackage[left=19mm,right=19mm,top=20mm,bottom=22mm]{geometry}
\usepackage{graphicx, amsmath, amsthm, amssymb}
\setcounter{MaxMatrixCols}{20}
\setlength{\textheight}{260mm}
\setlength{\textwidth}{170mm}
\usepackage[T1]{fontenc}

\makeatletter
\renewenvironment{proof}[1][\proofname]{\par
\pushQED{\qed}%
\normalfont \topsep6\p@\@plus6\p@\relax
\trivlist
\item[\hskip\labelsep
\bfseries\itshape
}{%
\popQED\endtrivlist\@endpefalse
}
\makeatother

\newtheoremstyle{italiktekst} %name
{5mm}    %Space above, empty = usual value'
{5mm}    %Space below
{\itshape}   %Body font
{}           %Indent amount (empty = no indent, \parindent = para indent) for head
{\newline}   %Space after thm head: \newline = linebreak

\theoremstyle{italiktekst}
\newtheorem{theorem}{Theorem}[section]
\newtheorem{lemma}[theorem]{Lemma}
\newtheorem{corollary}[theorem]{Corollary}
\newtheorem{proposition}[theorem]{Proposition}
\newtheorem{problem}[theorem]{Problem}

\renewcommand{\thesection}{\arabic{section}.}
\renewcommand{\thetheorem}{\thesection\arabic{theorem}}

\setcounter{page}{5}
\begin{document}
\setcounter{section}{-1}
\raggedright

\section{\rm Perron-Frobenius theorem}

\begin{lemma}
\hspace*{5mm}
\label{U_Ainvariant_UT_Ainvariant}
Let $\langle \cdot, \cdot\rangle$ be the standard inner product for ...
\end{lemma}

\begin{proof}
Recall that for a subspace $\mathcal{U}$ is said to be ...
\end{proof}

\begin{lemma}
\hspace*{5mm}
\label{columns_independent_AP_PD}
Consider arbitrary rectangular matrix $P$ of order
$m\times n$ in which columns are linearly independent.
The column space ...
\end{lemma}

\begin{proof}
Denote by $\mathcal{M}$ column
space ...
\end{proof}

...

\vspace*{5mm}
Recall that, from Lemma \ref{U_Ainvariant_UT_Ainvariant} we have...

\vspace*{5mm}...in Lemma \ref{columns_independent_AP_PD} we have shown that...

\end{document}
`
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This is so good that I would cry. Thank you. –  user27025 Mar 8 '13 at 7:09