# Writing a theorem inside a theorem

I want to write couple of theorems inside a main theorem body. In particular I want to write something like the following:

I tried using the command \newtheorem to create Main Theorem and then used the command \begin{theorem} inside it but it doesn't serve the purpose. I want something like this to be specific: Thanks for the help!!

• What about this code that produces this layout? Apart from some formatting, it works as a possible layout for your problem. Can you elaborate on the areas you're struggling with? – Werner Dec 1 '18 at 23:49
• i'd be inclined to enter this as \subsection*{Main theorem} \textit{...} \begin{theorem} ... \end{theorem} and avoid the hassle of nesting. since \ref{...} will be shown the same way regardless of what it refers to (unless you're using \cref), a reader shouldn't notice the difference. – barbara beeton Dec 2 '18 at 2:53
• The main should be without number and the sub-theorem with a within-section numbering? Do you have to refer both to the main and the sub-theorems? Do you have a list of theorems? How should they appear in it? – CarLaTeX Dec 2 '18 at 6:02
• I want exactly two sub-theorems, let's say Theorem A and Theorem B under the main theorem. The main theorem should be without number and I would like to refer to the sub theorems. – tattwamasi amrutam Dec 2 '18 at 6:09

Here's an implementation using enumitem.

\documentclass{article}
\usepackage{amsmath}
\usepackage{amsthm}
\usepackage{enumitem}

\usepackage{lipsum}

\newtheorem{theorem}{Theorem}[section]
\newtheorem*{main}{Main Theorem}

\newenvironment{subtheorems}
{\itemize[
nosep,font=\normalfont\bfseries,
leftmargin=3em,itemindent=-1em,align=left]}
{\enditemize}

\begin{document}

\section{Introduction}

\lipsum[2]

\begin{main}
We obtain the following bijective correspondences.
\begin{subtheorems}
\item[$\mathbf{C}^*$-case (Theorem \ref{C*case}):]
Let $\Gamma$ be a discrete group \lipsum*[3]

\item[$\mathbf{W}^*$-case (Theorem \ref{W*case}):]
Let $\Gamma$ be a countable group \lipsum[4]
\end{subtheorems}
\end{main}

\lipsum

\setcounter{section}{2}\setcounter{theorem}{2}
\begin{theorem}\label{C*case}
Text
\end{theorem}

\setcounter{section}{3}\setcounter{theorem}{5}
\begin{theorem}\label{W*case}
Text
\end{theorem}

\end{document}


A different realization, with numbered subtheorems.

\documentclass{article}
\usepackage{amsmath}
\usepackage{amsthm}
\usepackage{enumitem}

\usepackage{lipsum}

\newtheorem{theorem}{Theorem}[section]
\newtheorem*{main}{Main Theorem}

\newenvironment{subtheorems}
{\enumerate[
label=Theorem \Alph*\protect\thissubtheorem,
ref=\Alph*,
font=\normalfont\bfseries,
leftmargin=0pt,itemindent=!,
align=left,
]}
{\endenumerate}
\newcommand{\thissubtheorem}{}
\newcommand{\subtheorem}[1][]{%
\if\relax\detokenize{#1}\relax
\def\thissubtheorem{}%
\else
\def\thissubtheorem{ (#1)}%
\fi
\item
}

\begin{document}

\section{Introduction}

\lipsum[2]

\begin{main}
We obtain the following bijective correspondences.
\begin{subtheorems}
\subtheorem[$\mathbf{C}^*$-case]\label{C*case}
Let $\Gamma$ be a discrete group \lipsum*[3]

\subtheorem[$\mathbf{W}^*$-case]\label{W*case}
Let $\Gamma$ be a countable group \lipsum[4]
\end{subtheorems}
\end{main}

Theorem~\ref{C*case} and theorem~\ref{W*case} are important.

\end{document}


• What if I want to just call them Theorem A and Theorem B and refer to them? How do I do that? I don't want the counter to depend on section, for I want to keep them in the same section. – tattwamasi amrutam Dec 2 '18 at 22:06
• @tattwamasiamrutam I added a possible solution based on your picture, but I don't see any usefulness for it. – egreg Dec 2 '18 at 22:22
• Hi, thanks for the help, I just want to keep it in the same section because they are pretty much similar, but are in different contexts. Their proofs are also similar except for some minor modifications here and there. I just want to convey that they are similar in many respects and talk about same things from different view point – tattwamasi amrutam Dec 2 '18 at 22:33