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  "body": "\n## Summary\n\nA strongly regular graph is a [[regular graph|0Q70YFB6ZM]] with a second kind of regularity.\nThe number of common neighbours of two distinct vertices depends only on whether they are adjacent.\nIts parameters are written $(v, k, \\lambda, \\mu)$.\nA connected strongly regular graph that is not complete has exactly three distinct adjacency eigenvalues.\nThese graphs are a meeting point of graph theory, design theory and group theory.\nThe node [[strongly regular graph|J50MA9C0EH]] gives the precise definition.\n\n## Explanations\n\n### L1 human\n\nIn a strongly regular graph every vertex has the same number of neighbours.\nMoreover, any two friends have the same number of common friends, and any two strangers have the same number of common friends.\nThe pentagon $C_5$ is an example: two adjacent vertices have no common neighbour, and two non-adjacent vertices have exactly one.\nThe [[Petersen graph|0NR95CTFCZ]] is a larger example.\n",
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