How to get hyperref to differentiate between similarly numbered theorems?

Question

I am writing a book in which theorems are numbered "Theorem 1", "Theorem 2", etc. in every chapter; the resetting of the Theorem counter is done using an explicit \setcounter command. When I intend to point at Theorem 1 of any chapter using hyperref, the link created points to Theorem 1 of Chapter 1 instead (see MWE below).

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{hyperref}
\newtheorem{theorem}{Theorem}

\begin{document}

\begin{theorem}[First]\label{thm1}
The first.
\end{theorem}

\newpage

\setcounter{theorem}{0}

\begin{theorem}[Second]\label{thm2}
The second.
\end{theorem}

Reference to the second occurrence of Theorem 1 : \ref{thm2}.
\end{document}

I know I could certainly fix this issue by numbering theorems including a chapter number (like "Theorem 1.1"), but I like the simpler numbering better. Is there a way to convince hyperref to distinguish between the two theorems above (and therefore to point properly to the second one) even if the numbering displayed is the same?

Thank you in advance!

Piotr

Answer 1

I don't think it's nice to your readers having to see “as proved in theorem 8 of chapter 11” instead of the simpler “as proved in theorem 11.8”.

Anyway, you don't need to manually reset the counter and you can change the H-representation of the counter to get a unique anchor.

\documentclass{book}
\usepackage{hyperref}

\newtheorem{theorem}{Theorem}
\counterwithin*{theorem}{chapter}
\renewcommand{\theHtheorem}{\thechapter.\arabic{theorem}}

\begin{document}

\chapter{First}

\begin{theorem}[First]\label{thm1}
The first.
\end{theorem}

\chapter{Second}

\begin{theorem}[Second]\label{thm2}
The second.
\end{theorem}

Reference to the first occurrence of Theorem 1: \ref{thm1}.

Reference to the second occurrence of Theorem 1: \ref{thm2}.

\end{document}

You'll see that the first link points to chapter 1 and the second link to chapter 2.