\item \BDDToROBDD

\begin{center}
\begin{forest}
for tree={circle, draw, no edge,
            minimum size=2em,
            inner sep=0pt,
            s sep=5mm,
            l sep=5mm}
[$f$, rectangle, draw,  tikz={\draw [line] () to (a.north);}
    [$a$, name=a, tikz={\draw [line, bend right] () to (b.north west); \draw [fulldot=.5, bend left] () to (b.north east);}
        [$b$, name=b, tikz={\draw [line] () to (c1.north); \draw [dot=.5] () to (c2.north);}
            [$c$, name=c1, tikz={\draw [line] () to (256:4.6); \draw [fulldot=.5] () to (268:4.5);}]
            [$c$, name=c2, tikz={\draw [line] () to (272:4.5); \draw [fulldot=.5] () to (284:4.6);}]
        ]
    ]
]
\end{forest}
\end{center}