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  "body": "\n## Summary\n\nIn mathematics, **Johnson graphs** are a special class of undirected graphs defined from systems of sets. The vertices of the Johnson graph $J(n,k)$ are the $k$-element [[subsets|0BJR9QR08E]] of an $n$-element set; two vertices are adjacent when the [[intersection|0ZNMMA9TF5]] of the two vertices (subsets) contains $(k-1)$-elements. Both Johnson graphs and the closely related Johnson scheme are named after Selmer M. Johnson.\n",
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