# This simple code just won't compile

This is the code:

\documentclass{article}

\usepackage{amsthm}

\begin{document}
\begin{proof}
\end{proof}
\end{document}


This is the error I get:

This is pdfTeX, Version 3.14159265-2.6-1.40.19 (TeX Live 2018/W32TeX) (preloaded format=pdflatex 2018.12.17) 3 JUN 2020 17:21 entering extended mode restricted \write18 enabled. %&-line parsing enabled. **document.tex (./document.tex LaTeX2e <2018-12-01> (c:/texlive/2018/texmf-dist/tex/latex/base/article.cls Document Class: article 2018/09/03 v1.4i Standard LaTeX document class (c:/texlive/2018/texmf-dist/tex/latex/base/size10.clo File: size10.clo 2018/09/03 v1.4i Standard LaTeX file (size option) ) \c@part=\count80 \c@section=\count81 \c@subsection=\count82 \c@subsubsection=\count83 \c@paragraph=\count84 \c@subparagraph=\count85 \c@figure=\count86 \c@table=\count87 \abovecaptionskip=\skip41 \belowcaptionskip=\skip42 \bibindent=\dimen102 ) (c:/texlive/2018/texmf-dist/tex/latex/amscls/amsthm.sty Package: amsthm 2017/10/31 v2.20.4 \thm@style=\toks14 \thm@bodyfont=\toks15 \thm@headfont=\toks16 \thm@notefont=\toks17 \thm@headpunct=\toks18 \thm@preskip=\skip43 \thm@postskip=\skip44 \thm@headsep=\skip45 \dth@everypar=\toks19 ) (./document.aux) \openout1 = document.aux'.

LaTeX Font Info: Checking defaults for OML/cmm/m/it on input line 5. LaTeX Font Info: ... okay on input line 5. LaTeX Font Info: Checking defaults for T1/cmr/m/n on input line 5. LaTeX Font Info:
... okay on input line 5. LaTeX Font Info: Checking defaults for OT1/cmr/m/n on input line 5. LaTeX Font Info: ... okay on input line 5. LaTeX Font Info: Checking defaults for OMS/cmsy/m/n on input line 5. LaTeX Font Info: ... okay on input line 5. LaTeX Font Info: Checking defaults for OMX/cmex/m/n on input line 5. LaTeX Font Info: ... okay on input line 5. LaTeX Font Info: Checking defaults for U/cmr/m/n on input line 5. LaTeX Font Info: ... okay on input line 5.

! Undefined control sequence. \qedsymbol ->\openbox l.7 \end{proof} The control sequence at the end of the top line of your error message was never \def'ed. If you have misspelled it (e.g., \hobx'), typeI' and the correct spelling (e.g., I\hbox'). Otherwise just continue, and I'll forget about whatever was undefined.

[1

{c:/texlive/2018/texmf-var/fonts/map/pdftex/updmap/pdftex.map}] (./document.aux) ) Here is how much of TeX's memory you used: 301 strings out of 492616 3273 string characters out of 6132767 60701 words of memory out of 5000000 4294 multiletter control sequences out of 15000+600000 3986 words of font info for 15 fonts, out of 8000000 for 9000 1141 hyphenation exceptions out of 8191 23i,4n,17p,116b,107s stack positions out of 5000i,500n,10000p,200000b,80000s Output written on document.pdf (1 page, 17026 bytes). PDF statistics: 16 PDF objects out of 1000 (max. 8388607) 10 compressed objects within 1 object stream 0 named destinations out of 1000 (max. 500000) 1 words of extra memory for PDF output out of 10000 (max. 10000000)

This code is working though:

\documentclass{article}

\usepackage{newpxmath}
\usepackage{amsthm}

\begin{document}
\begin{proof}
\end{proof}
\end{document}


What's going on here?

Edit: this is what I see in my editor.

• The first one works for me, but the second one doesn't. To make the second work you need to load amsthm first. – Phelype Oleinik Jun 3 '20 at 15:54
• For some reason the first one doesn't work for me and the second one works whether amsthm comes first or newpxmath does... – Lele99_DD Jun 3 '20 at 16:13
• Apparently, everything works fine as long as I don't use the "proof" environment without the newpxmath package. – Lele99_DD Jun 3 '20 at 16:40
• Sorry, but I can only confirm Phelype's finding: the first code compiles, the second doesn't. I tried with TeX Live 2018. Can you please paste again the log file, but using the code markup just like for the sample documents? – egreg Jun 3 '20 at 17:42
• @egreg I've edited my post, but I'm not sure that is what you're looking for. Is it helpful? – Lele99_DD Jun 3 '20 at 17:52