# Number/Letter Theorem

Is there any way from the code below that a number letter/number theorem can be generated? I am trying to achieve a theorem labeled 1.1A.

\documentclass{book}
\usepackage{amsthm}

\newtheorem{theo}{Theorem}[chapter]
\newcounter{tmp}

\begin{document}

\chapter{Test Chapter}
\begin{theo}
test
\end{theo}

\begingroup
\setcounter{tmp}{\value{theo}}% store current value of theorem counter
\setcounter{theo}{0} %assign desired value to theorem counter
\renewcommand\thetheo{\Alph{theo}}% locally redefine the representation of    the theorem counter
\begin{theo}
test
\end{theo}
\endgroup

\end{document}

• – egreg Mar 9 '16 at 21:06
• Is the inner theo a sub theorem then? What should 1.1a indicate. Subtheorem a of theorem 1.1? I don't think the group is really necessary – user31729 Mar 9 '16 at 21:07
• I'm afraid your write-up isn't very clear. Currently, your code generates two theorem-like environments, labelled "Theorem 1.1" and "Theorem A". Please be more specific as to what you're trying to achieve. – Mico Mar 9 '16 at 21:08
• apologies.. i am trying to achieve a theorem labeled 1.1A – coder123 Mar 9 '16 at 21:09
• @coder123: If you're wanting to provide a slight variation of Theorem 1.1, you could use Theorem 1.1'. Could you describe what you're after in better detail? – Werner Mar 9 '16 at 21:15

In my opinion, a 2nd theorem environment which 'depends' on the upper level environment theo is a cleaner solution than to use \begingroup...\endgroup etc. and storing the counter, changing the output etc.

\documentclass{book}
\usepackage{amsthm}

\newtheorem{theo}{Theorem}[chapter]

\newtheorem{subtheo}{Subheorem}[theo] % Use theo as driver counter
\renewcommand{\thesubtheo}{\thetheo\Alph{subtheo}} % Change subtheo counter for alpha output

\begin{document}

\chapter{Test Chapter}
\begin{theo}
test
\end{theo}

\begin{subtheo}
test
\end{subtheo}

\end{document}