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\begin{center}\begin{forest}for tree={circle, draw, no edge, minimum size=2em, inner sep=0pt, s sep=2mm, l sep=4mm}[$f$, rectangle, draw, tikz={\draw [line] () to (a.north);} [$a$, name=a, tikz={\draw [line] () to node[pos=.7, above] {\scriptsize T \;} (b.north east); \draw [dot=.5] () to node[pos=.5, above] {\; \scriptsize E} (c2.north west);} [$b$, name=b, tikz={\draw [dot=.5, bend left] () to node[pos=.5, right] {\scriptsize E \;} (c1.north east); \draw [line, bend right] () to node[pos=.5, left] {\; \scriptsize T} (c1.north west);} [$c$, name=c1, s sep=20mm, tikz={\draw [line] () to node[pos=.7, left] {\scriptsize T \;} (one.north); \draw [dot=.5] () to node[pos=.5, above] {\; \scriptsize E} (e.north west);} [,phantom] [$e$, name=e, s sep=10mm, tikz={\draw [line, bend left] () to node[pos=.7, above] {\scriptsize T \;} (one.north east); \draw [dot=.5, bend left] () to node[pos=.2, below] {\; \scriptsize E} (one.east);} [$1$, rectangle, draw, name=one] [$0$, rectangle, draw, name=zero] ] ] ] [$c$, name=c2, tikz={\draw [line, bend right] () to node[pos=.3, above] {\scriptsize T \;} (e.north); \draw [dot=.5, bend left] () to node[pos=.5, above] {\; \scriptsize E} (d.north);} [,phantom] [$d$, name=d, tikz={\draw [line] () to node[pos=.7, above] {\scriptsize T \;} (e.north east); \draw[dot=.5] () to node[pos=.3, below] {\; \scriptsize E} (zero.north);} [,phantom] [,phantom] ] ] ]]\end{forest}\end{center}
A binary decision diagram represents a Boolean formula $f$. It is a DAG with two terminal nodes that arelabelled with 0 and 1. The internal nodes are labelled with the Boolean variablesof the formula (here a, b, c, d and e). Each internal node has exactly two outgoingedges: one edge labeled with a T (the then-edge), and another edge thatis labeled with an E (the else-edge) or marked with a circle. There is a uniqueinitial node called the function node labeled with $f$ that does not have any incoming edges and one outgoing edge to the internal variable node on the firstlevel.
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