Btukfyl

Here is a minimal example:

documentclass{amsart}



usepackage{amsthm}

usepackage[pdftex]{hyperref}



newtheoremstyle{myexercise}{baselineskip}{baselineskip}{}{}{bfseries}{.}{ }{thmname{#1}thmnumber{ #2}thmnote{ (#3)}}

newtheoremstyle{mypart}{baselineskip}{baselineskip}{}{}{bfseries}{}{newline}{thmname{#1}thmnumber{ #2}thmnote{ -- #3}}



theoremstyle{myexercise}

newtheorem{Exo}{Exercise}

theoremstyle{mypart}

newtheorem{Part}{Part}[Exo]

renewcommand*thePart{Roman{Part}}



begin{document}

begin{Exo}[A cool exercise]

begin{Part}

label{p:ex1:I}

Prove that $1=0$.

end{Part}

begin{Part}

Deduce from Part~ref{p:ex1:I} that this exercise is wrong.

end{Part}

end{Exo}



begin{Exo}

begin{Part}

Let $a=b$. Deduce that $0=0$.

end{Part}

begin{Part}

Let $a=42$. For what values of $b$ do we have $a=b$?

end{Part}

end{Exo}

end{document}

The warning I get is the following:

pdf TeX warning (ext4): destination
with the same identifier
(name{Part.1.1}) has b een already
used, duplicate ignored

AtBegShi@Output ...ipout box
AtBeginShipoutBox
fi fi l.35 end{document}
pdfTeX warning (ext4): destination with the same
identifier (name{Part.2.1}) has been
already used, duplicate ignored

AtBegShi@Output ...ipout box
AtBeginShipoutBox
fi fi l.35 end{document}
] (./TestHyperref.aux) )

This looks like a strange behavior to me. Or have I done anything wrong?

Besides, the error completely disappears if I use, e.g., enumerates inside the Part environment, as in

...

begin{Part}

begin{enumerate}

item Prove that $1=0$.

end{enumerate}

end{Part}

...

Also, there's no error if I remove the hyperref package. Unfortunately, I need to use hyperref.

Any idea?

It's possible to use nested theorems with article.cls and ntheorem, now the problem seems to come from a conflict between amsart and hyperref. ntheorem has an option to avoid compatibility with hyperref.

documentclass{article}

usepackage[pdftex]{hyperref}

usepackage[hyperref]{ntheorem}  



newtheorem{Exo}{Exercise}

newtheorem{Part}{Part}[Exo]

renewcommand*thePart{Roman{Part}} 



begin{document} 

begin{Exo}[A cool exercise]

begin{Part}

label{p:ex1:I}

Prove that $1=0$.

end{Part}

begin{Part}

Deduce from Part~ref{p:ex1:I} that this exercise is wrong.

end{Part}

end{Exo}



begin{Exo}

begin{Part}

Let $a=b$. Deduce that $0=0$.

end{Part}

begin{Part}

Let $a=42$. For what values of $b$ do we have $a=b$?

end{Part}

end{Exo} 

end{document}

The problem seems to be between amsartand hyperref.

After a lot of search, I finally found a simple solution: load hyperref before any ams package. Replacing the amsart document class by article class and pulling the hyperref package above the amsthm one solved my problem.

It does not always work, though. It can reduce the number of such warnings, and in some cases make them disappear.

For those who do want to use the amsart class that is still not a solution, though...

I had this problem (seemingly) and found that the cause was not having loaded the siunitx package. I don't know why it had that effect, but it did.

try

usepackage[hypertexnames=false]{hyperref}