app.log

This is pdfTeX, Version 3.141592653-2.6-1.40.23 (MiKTeX 21.8) (preloaded format=pdflatex 2021.10.3)  1 DEC 2021 10:04
entering extended mode
**./app.tex
(app.tex
LaTeX2e <2021-06-01> patch level 1
L3 programming layer <2021-08-27>
! Undefined control sequence.
l.1 \appendix
             
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'), type `I' and the correct
spelling (e.g., `I\hbox'). Otherwise just continue,
and I'll forget about whatever was undefined.


! LaTeX Error: Command \@makechapterhead undefined.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...                                              
                                                  
l.5 \renewcommand{\@makechapterhead}
                                    [1]{\vspace *{-10\p@ }{\parindent \z@
Try typing  <return>  to proceed.
If that doesn't work, type  X <return>  to quit.

)
! Emergency stop.
<*> ./app.tex
             
*** (job aborted, no legal \end found)

 
Here is how much of TeX's memory you used:
 21 strings out of 478927
 495 string characters out of 2850605
 290175 words of memory out of 3000000
 17981 multiletter control sequences out of 15000+600000
 403430 words of font info for 27 fonts, out of 8000000 for 9000
 1141 hyphenation exceptions out of 8191
 13i,0n,12p,98b,14s stack positions out of 5000i,500n,10000p,200000b,80000s
!  ==> Fatal error occurred, no output PDF file produced!