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2 of 3 typo fix

Adapting the code posted Werner's answer to the posting How to remove line breaks before and after theorems?, one could set up a theorem-like environment, called shortthm, that shares a counter with the "main" theorem counter but doesn't feature a line break (and other spacing factors).

enter image description here

\documentclass[12pt,letterpaper]{article}
\usepackage{amsmath,amsthm}
\newtheorem{theorem}{Theorem} % main theorem-like environment

\makeatletter
\newenvironment{shortthm}{%
    \refstepcounter{theorem}
    \textbf{Theorem~\thetheorem.}%
    \space\em}{% 
    \par}
\makeatother

\begin{document}

\begin{enumerate}
    \item
        \begin{theorem}
            $a^2 + b^2 = c^2$.
        \end{theorem}
    \item 
        \begin{theorem}
            $E=mc^2$.
        \end{theorem}
\end{enumerate}

\dots

\begin{enumerate}
    \item
        \begin{shortthm}
            $a^2 + b^2 = c^2$.
        \end{shortthm}
    \item 
        \begin{shortthm}
            $E=mc^2$.
        \end{shortthm}
\end{enumerate}

\begin{theorem} Some other theorem\dots \end{theorem}

\end{document}