A boolean circuit $f(x_1,\ldots,x_n)$ \emph{represents} a graph $G$ on $n$ vertices if for every input vector $a\in\{0,1\}^n$ with precisely two $1$'s in, say, positions $i$ and $j$, $f(a)=1$ precisely when $i$ and $j$ are adjacent in $G$; on inputs with more or less than two $1$'s the circuit can output ...
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