This is pdfTeX, Version 3.14159265-2.6-1.40.16 (TeX Live 2015/Debian) (preloaded format=latex 2019.6.6)  22 OCT 2020 12:34
entering extended mode
 restricted \write18 enabled.
 %&-line parsing enabled.
**\begin{document}$x - \mu$\end{document}
No file texput.aux.
\openout1 = `texput.aux'.

LaTeX Font Info:    Checking defaults for OML/cmm/m/it on input line 0.
LaTeX Font Info:    ... okay on input line 0.
LaTeX Font Info:    Checking defaults for T1/cmr/m/n on input line 0.
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LaTeX Font Info:    Checking defaults for OT1/cmr/m/n on input line 0.
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LaTeX Font Info:    Checking defaults for OMS/cmsy/m/n on input line 0.
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LaTeX Font Info:    Checking defaults for OMX/cmex/m/n on input line 0.
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! LaTeX Error: The font size command \normalsize is not defined:
               there is probably something wrong with the class file.

See the LaTeX manual or LaTeX Companion for explanation.
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 ...                                              
                                                  
<*> \begin{document}
                    $x - \mu$\end{document}
? X
 
Here is how much of TeX's memory you used:
 3 strings out of 493030
 329 string characters out of 6136261
 53056 words of memory out of 5000000
 3641 multiletter control sequences out of 15000+600000
 3640 words of font info for 14 fonts, out of 8000000 for 9000
 1141 hyphenation exceptions out of 8191
 7i,0n,6p,54b,28s stack positions out of 5000i,500n,10000p,200000b,80000s
No pages of output.