diff --git a/assignments/main_text.pdf b/assignments/main_text.pdf index 1615538..4899454 100644 Binary files a/assignments/main_text.pdf and b/assignments/main_text.pdf differ diff --git a/assignments/template b/assignments/template index 7b85d98..de9419d 160000 --- a/assignments/template +++ b/assignments/template @@ -1 +1 @@ -Subproject commit 7b85d987143e4d5c71a12cd116811ce6d0be0bf5 +Subproject commit de9419d4cc22f8204a8d49376bd5e507efa01a43 diff --git a/assignments/week1/1.pdf b/assignments/week1/1.pdf index 41e6977..6b523de 100644 Binary files a/assignments/week1/1.pdf and b/assignments/week1/1.pdf differ diff --git a/assignments/week1/1.tex b/assignments/week1/1.tex index a012809..0b37136 100644 --- a/assignments/week1/1.tex +++ b/assignments/week1/1.tex @@ -1,6 +1,8 @@ \documentclass[../main_text.tex]{subfiles} \begin{document} +\section*{Week 1} + \exercise*[0.3.6] \begin{enumerate}[label=\emph{\alph*)}] \item Wanting to show: @@ -8,15 +10,40 @@ In order to prove this equivalence, we have to prove the implication both ways. We use two lemmas for this. - \begin{lemma}[test] + \begin{lemma} + \label{lem:set1} $A \cap (B \cup C) \implies (A \cap B) \cup (A \cap C)$ - - Let $x \in A \cap (B \cup C)$. \end{lemma} - \begin{definition} - Test. - \end{definition} - \item + + Let $x \in A \cap (B \cup C)$. + By the definition of set intersection, $x \in A$ and $x \in B \cup C$. + By the definition of set union, $x \in A$ and $(x \in B$ or $x \in C)$. + From propositional logic we know that for propositions $P$, $Q$ and $R$ the following holds: + $P \land (Q \lor R) \iff (P \land Q) \lor (P \land R)$. + So, substituting for this particular case yields $(x \in A$ and $x \in B)$ or $(x \in A$ and $x \in C)$. + Using the definition of set intersection again gets $x \in A \cap B$ or $x \in A \cap C$. + Using the definition of set union again gives $x \in (A \cap B) \cup (A \cap C)$. \qed + + \begin{lemma} + \label{lem:set2} + $(A \cap B) \cup (A \cap C) \implies A \cap (B \cup C)$ + \end{lemma} + Let $x \in (A \cap B) \cup (A \cap C)$. + By the definition of set union, $x \in (A \cap B)$ or $x \in (A \cap C)$. + By the definition of set intersection, $(x \in A$ or $x \in B)$ and $(x \in A$ or $x \in B)$. + Using the same propositional logical equivalence as in Lemma \ref{lem:set1}, this gives + $x \in A$ and $(x \in B$ or $x \in C)$. + Wrapping up, we use the definition of set union to get $x \in A$ and $x \in B \cup C$ and + the definition of intersection to get $x \in A \cap (B \cup C)$. \qed + + Using Lemma \ref{lem:set1} and \ref{lem:set2}, we get the desired equivalence of + $A \cap (B \cup C) = (A \cap B) \cup (A \cap C)$. \qed + \item Wanting to show: + $A \cup (B \cap C) = (A \cup B) \cap (a \cup C)$ + + This proof is so similar to a) that it feels like a waste of time and will therefore be left to the reader. \end{enumerate} +\hrule + \end{document}