\section{A nonlinear recurrence: many faces of Catalan numbers}\label{catalan} 

Hallo

\subsection{Triangulations of a polygon}

\subsection{Recurrence relation for triangulations}

\subsection{The cashier problem}

\subsection{Dyck paths}

\subsection{Recurrence relations for Dyck paths}

\subsection{Reflection trick and a formula for Catalan numbers}

\subsection{Binary trees}

\subsection{Exercises}