## AbstractWe study the size of OBDDs (ordered binary decision diagrams) for representing the adjacency function $f_G$ of a graph $G$ on $n$ vertices. Our results are as follows: - for graphs of bounded tree-width there is an OBDD of size $O(\log{n})$ for $f_G$ that uses encodings of size $O(\log{n})$ for the vertices; - for graphs of bounded clique-width there is an OBDD of size $O(n) $ for $f_G$ that uses encodings of size $O(n)$ for the vertices; - for graphs of bounded clique-width such that there is a \emph{reduced term} for $G$ (to be defined below) that is balanced with depth $O(\log{n})$ there is an OBDD of size $O(n) $ for $f_G$ that uses encodings of size $O(\log{n})$ for the vertices; - for cographs, i.e. graphs of clique-width at most 2, there is an OBDD of size $O(n)$ for $f_G$ that uses encodings of size $O(\log{n})$ for the vertices. This last result improves a recent result by Nunkesser and Woelfel \cite{Nunkesser}.
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