FIX add missing proposition thm style

theoremstyles.tex

@@ -3,6 +3,7 @@
 \newtheorem{theorem}{Theorem}[section]
 \newtheorem{corollary}{Corollary}[section]
 \newtheorem{lemma}{Lemma}[section]
+\newtheorem{proposition}{Proposition}[section]
 \newtheorem{example}{Example}[section]
 
 \theoremstyle{definition}