diff --git a/main.tex b/main.tex
index a705871..32ac155 100644
--- a/main.tex
+++ b/main.tex
@@ -36,16 +36,18 @@
 \usepackage{enumerate}
 
 \usepackage{amsmath, amssymb, mathrsfs}
-\usepackage{amsthm}
+\usepackage{amsthm} % For theorem style
+\usepackage{thmtools}
+\usepackage{thm-restate}
+\usepackage[capitalise]{cleveref}
 \usepackage{comment}
 \usepackage{tikz}
 \usetikzlibrary{positioning,patterns,shapes}
 
 % theorems, definitions
-\newtheorem{theorem}{Theorem}[chapter]
-\newtheorem{lemma}{Lemma}[chapter]
-\theoremstyle{definition}
-\newtheorem{definition}{Definition}[chapter]
+\declaretheorem[numberwithin=chapter]{theorem}
+\declaretheorem[sibling=theorem]{lemma}
+\declaretheorem[numberwithin=chapter,style=definition]{definition}
 
 \usepackage{pdfpages}
 \usepackage{xspace}