\documentclass[../main_text.tex]{subfiles} \begin{document} \exercise*[0.3.6] \begin{enumerate}[label=\emph{\alph*)}] \item Wanting to show: $A \cap (B \cup C) = (A \cap B) \cup (A \cap C)$ In order to prove this equivalence, we have to prove the implication both ways. We use two lemmas for this. \begin{lemma}[test] $A \cap (B \cup C) \implies (A \cap B) \cup (A \cap C)$ Let $x \in A \cap (B \cup C)$. \end{lemma} \begin{definition} Test. \end{definition} \item \end{enumerate} \end{document}