\begin{minipage}{0.5\textwidth}
\begin{tabbing}
$f$ \= $= (p \leftrightarrow q) \land (r \leftrightarrow s)$\\
	\>$ f_r $ \= $= (p \leftrightarrow q) \land s$ \\
	    \>\>$ f_{rs} $ \= $= (p \leftrightarrow q)$ \\
	        \>\>\>$ f_{rsp} $ \= $= q$ \\
	            \>\>\>\>$ f_{rspq} $ \= $= \top$ \\
	            \>\>\>\>$ f_{rsp \lnot q} $ \= $= \bot$ \\
	        \>\>\>$ f_{rs \lnot p} $ \= $= \lnot q = \lnot f_{rsp}$ \\
        \>\>$ f_{r \lnot s} $ \= $= \bot$ \\
	\>$ f_{\lnot r} = (p \leftrightarrow q) \land \lnot s$ \\
	    \>\>$ f_{\lnot rs} $ \= $= \bot$ \\
	    \>\>$ f_{\lnot r \lnot s} $ \= $= (p \leftrightarrow q) = f_{rs}$ \\
\end{tabbing}
\end{minipage}
\begin{minipage}{0.5\textwidth}
The final ROBDD:
\begin{center}
\begin{forest}
for tree={circle, draw, no edge,
            minimum size=2em,
            inner sep=0pt,
            s sep=6mm,
            l sep=6mm}
[$f$, rectangle, draw,  tikz={\draw [line] () to (r.north);}
    [$f_r$, rectangle, draw,  tikz={\draw [line] () to (s1.north west);}]
    [$r$, name=r, tikz={\draw [line] () to (s1.north); \draw [fulldot=.5] () to (s2.north);}
        [$f_{\lnot r \lnot s}$, rectangle, draw,  tikz={\draw [line] () to (p.north west);}]
        [$f_{rs}$ , rectangle, draw,  tikz={\draw [line] () to (p.north west);}]
        [$s$, name=s1, tikz={\draw [line] () to (p.north); \draw [fulldot=.5] () to (-0.2, -3.5);}
            [$f_{\lnot rsp}$, rectangle, draw,  tikz={\draw [line] () to (q.north west);}]
            [$p$, name=p, tikz={\draw [line, bend right=14] () to (q.north); \draw [fulldot=.5, bend left=14] () to (q.north east);}
                [$q$, name=q, tikz={\draw [line] () to (-2.3, -6.2); \draw [fulldot=.5] () to (-1.5, -6.2);}
                ]
                [,phantom]
            ]
            [,phantom]
            [,phantom]
        ]
        [$s$, name=s2, tikz={\draw [line] () to (0.2,-3.5); \draw [fulldot=.5, bend left=70] () to (p.east);}]
        [,phantom]
        [,phantom]
    ]
    [$f_{\lnot r}$, rectangle, draw,  tikz={\draw [fulldot=.5] () to (s2.north east);}]
]
\end{forest}
\end{center}

\end{minipage}