Prevent word break in word Big O

report/parts/theory.tex

@@ -284,7 +284,7 @@ \subsubsection{Bachmann-Landau Notation}
       \addplot[draw=none] coordinates {(0,-0.5)};
     \end{axis}
   \end{tikzpicture}
-  \caption{Example of Big O notation, the function $f(x)$ is $O(n)$, but $g(x)$ is not.}
+  \caption{Example of Big~O notation, the function $f(x)$ is $O(n)$, but $g(x)$ is not.}
   \label{fig:big-o-visualization}
 \end{figure}