# Recent questions tagged dual-function

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The dual of a Boolean function $F(x_1,x_2,\dots,x_n,+, .,')$, written as $F^D$ is the same expression as that of $F$ with $+$ and $⋅$ swapped. $F$ is said to be self-dual if $F = F^D$. The number of self-dual functions with $n$ Boolean variables is $2^n$ $2^{n-1}$ $2^{2^{n}}$ $2^{2^{n-1}}$