\item \self Construct a Reduced Ordered Binary Decision Diagram (ROBDD) for the formula 

$$f = (\neg a \vee b) \wedge (a \vee b),$$

using \textit{alphabetic variable order}. Use complemented edges and a node for \texttt{true} as the only constant node. To simplify drawing, you may assume that \textit{dangling edges} point to the constant node. Write down all cofactors that you compute to obtain the final result and mark them in the graph.

% (not a or b) and (a or b)