solved 1

Author: BelegCuthalion

preamble.tex

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+\usepackage{amsmath}
+\usepackage{amssymb}
+\usepackage{amsthm}
+\usepackage{tikz-cd}
+\usepackage{tikz}
+
+\usetikzlibrary{positioning}
+\theoremstyle{definition}
+\newtheorem{exc}[section]{Exercise}
+\newcommand{\exn}[1]{\setcounter{section}{#1}\addtocounter{section}{-1}\exc}
+\newcommand*{\ExcNum}{28}

solutions.tex

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+\documentclass[a4paper,12pt]{exam}
+\input{preamble}
+\begin{document}
+
+\foreach \c in {1,2,...,\ExcNum}{%
+  \IfFileExists{solutions/\c.tex} {%
+    \exn{\c} \input{solutions/\c.tex}%
+  }%
+}%
+\end{document}

solutions/1.tex

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+\quad
+\begin{center}\begin{tikzcd}
+  B \arrow[r, "g"] &
+  A \arrow[r, "h"]
+    \arrow["f_1"', loop, distance=2em, in=125, out=55]
+    \arrow["f_2"', loop, distance=2em, in=305, out=235] &
+  C
+\end{tikzcd}\end{center}
+  Let there be two such morphs $f_1$ and $f_2$, such that for all $g$, we have $f_1 g = g$, particularly $f_1 f_2 = f_2$, and we also have $h f_2 = h$, particularly $f_1 f_2 = f_1$. Obviously, we would have $f_1 = f_2$.