This is pdfTeX, Version 3.141592653-2.6-1.40.27 (MiKTeX 25.4) (preloaded format=latex 2025.9.2) 30 JAN 2026 17:56 entering extended mode \write18 enabled. %&-line parsing enabled. **./18-Memento-Python.tex (18-Memento-Python.tex LaTeX2e <2025-06-01> patch level 1 L3 programming layer <2025-07-11> ! Undefined control sequence. l.1 \simplechapter {Memento Python} 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: Missing \begin{document}. See the LaTeX manual or LaTeX Companion for explanation. Type H for immediate help. ... l.1 \simplechapter{M emento Python} You're in trouble here. Try typing to proceed. If that doesn't work, type X to quit. Missing character: There is no M in font nullfont! Missing character: There is no e in font nullfont! Missing character: There is no m in font nullfont! Missing character: There is no e in font nullfont! Missing character: There is no n in font nullfont! Missing character: There is no t in font nullfont! Missing character: There is no o in font nullfont! Missing character: There is no P in font nullfont! Missing character: There is no y in font nullfont! Missing character: There is no t in font nullfont! Missing character: There is no h in font nullfont! Missing character: There is no o in font nullfont! Missing character: There is no n in font nullfont! ) ! Emergency stop. <*> ./18-Memento-Python.tex *** (job aborted, no legal \end found) Here is how much of TeX's memory you used: 16 strings out of 468150 487 string characters out of 5429657 427005 words of memory out of 5000000 28717 multiletter control sequences out of 15000+600000 626825 words of font info for 40 fonts, out of 8000000 for 9000 1141 hyphenation exceptions out of 8191 15i,0n,18p,89b,18s stack positions out of 10000i,1000n,20000p,200000b,200000s No pages of output.