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From: ASND@TRIUMFRG.BITNET (Donald Arseneau)
Newsgroups: comp.text.tex
Subject: RE: Counters in List Environment
Message-ID: <0988B466B0000D2D@Post-Office.UH.EDU>
Date: 4 May 91 00:36:00 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Lines: 32

Yes, LaTeX does process the label in a list environment twice, which
can lead to double increments of counters.
 
The relevant definitions are:
 
\def\@item[#1]{ ...
...
\everypar{...
...
\setbox\@tempboxa\hbox{\makelabel{#1}}%
\global\setbox\@labels
 \hbox{\unhbox\@labels \hskip \itemindent
       \hskip -\labelwidth \hskip -\labelsep
       \ifdim \wd\@tempboxa >\labelwidth
                \box\@tempboxa
          \else \hbox to\labelwidth {\makelabel{#1}}\fi
       \hskip \labelsep}\ignorespaces}
 
It is clear that "#1" can be performed twice.
 
There is a safer way to handle the labels, and it is even more efficient!
I am surprised that it isn't what LaTeX does.
 
Replace the second-last line quoted above with:
 
          \else \hbox to\labelwidth {\unhbox\@tempboxa}\fi
 
Note: This is from an old version of LaTeX, so this MIGHT have been fixed!
 
Donald Arseneau
asnd@reg.triumf.ca
asnd@triumfcl