(./tex/lecture13.tex
! LaTeX Error: Command \threesim already defined.
Or name \end... illegal, see p.192 of the manual.
See the LaTeX manual or LaTeX Companion for explanation.
Type H <return> for immediate help.
...
l.3 ...ex\hbox{$\sim$}\vskip-.45ex\hbox{$\sim$}}}}
tex/lecture11.tex already defines \threesim; please move the definition to acs-category-theory-notes.tex and don't define it in either of the included files.
tex/lecture11.tex
already defines\threesim
; please move the definition toacs-category-theory-notes.tex
and don't define it in either of the included files.