Using amsthm to number examples - how do I account for altered examples (i.e. 1', 1'', etc.)

Question

I have sought long and hard for a solution to this and experimented with a combination of https://tex.stackexchange.com/a/43351 and https://tex.stackexchange.com/a/443, but could not get it to work. I would like the following to happen:

• I define an example somewhere in the text like this

  \begin{shortex}\label{Example1} lorem ipsum \end{shortex}
  

• Later in the document, I introduce an altered version of the example (Example 1'), if possible using cleveref

Here's my code before any of that happens:

\documentclass[letterpaper,12pt]{article} 

%Math symbol packages
  \usepackage{amsmath}
  \usepackage{amsfonts}
  \usepackage{amssymb}

%Add several formatting packages
  \usepackage{paralist}
  \usepackage[colorlinks=true,hidelinks]{hyperref}
  \usepackage{cleveref}
  \crefdefaultlabelformat{[#2#1#3]}

%Add theorem support
  \usepackage{amsthm}

%Define example
  \theoremstyle{definition}
  \newtheorem{ex}{Example}
  \renewcommand{\theex}{\arabic{ex}}

%Access package-internal code that uses @

\makeatletter

  % Define examples without linebreaks
  \newenvironment{shortex}
  {\refstepcounter{ex}\textsc{Example~}\theex:\normalfont}%\begin{shortex} 
    {}%\end{shortex}

\makeatother

%Define cref for Examples
  \crefname{ex}{}{examples}
  \creflabelformat{ex}{(#2#1#3)}

\begin{document}
   \begin{shortex}\label{ex1} This is example 1 \end{shortex}
\end{document}

I have tried getting rid of shortex and simply using {ex}, but this still wouldn't work.

Thanks for any help y'all can give!

EDIT (djupp): I also found David Carlisle's https://tex.stackexchange.com/a/69918/27148 now, which would probably work great if I could incorporate the suggested use of \ref (or \cref) to refer back to an older example. (I.e., it's possible that I would want to restate example 1 after I've already stated 2,3,4,5,etc.)

Answer 1

I don't know if this is what you're looking for; I define a varex environment for stating a variant of an example, computing its number via the label of the original one and a suffix that is, by default, a prime, but another one can be specified as optional argument.

\documentclass[letterpaper,12pt]{article} 

%Math symbol packages
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}

%Add theorem support
\usepackage{amsthm}

%Expanded references
\usepackage{refcount}

%Add several formatting packages
\usepackage{paralist}
\usepackage[colorlinks=true,hidelinks]{hyperref}
\usepackage{cleveref}
\crefdefaultlabelformat{[#2#1#3]}

%Define example
\theoremstyle{definition}
\newtheorem{ex}{Example}
\newcounter{Hex} % a new counter for hyperref

%Access package-internal code that uses @

\makeatletter
\g@addto@macro\ex{\stepcounter{Hex}} % use Hex for making anchors

% Define examples without linebreaks
\newenvironment{varex}[2][$'$]
  {\edef\theex{\getrefnumber{#2}#1}%
   \addtocounter{ex}{-1}
   \ex}
  {\endex}

\makeatother

%Define cref for Examples
  \crefname{ex}{example}{examples}
  \creflabelformat{ex}{(#2#1#3)}

\begin{document}
\begin{ex}\label{first}
An example.
\end{ex}

\begin{ex}\label{second}
Another one.
\end{ex}

\begin{varex}{first}\label{first'}
This is example 1$'$.
\end{varex}

\begin{varex}[$''$]{first}\label{first''}
This is example 1$''$.
\end{varex}

References:

\cref{first}

\cref{second}

\cref{first'}

\cref{first''}

\end{document}