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  "body": "\n## Example\n\nThe Petersen graph is the [[graph|0JD5C82QMB]] whose vertices are the $2$-element subsets of $\\{1, 2, 3, 4, 5\\}$.\nTwo vertices are adjacent if and only if they are disjoint subsets.\n\nIt has $\\binom{5}{2} = 10$ vertices and $15$ edges, and it is $3$-[[regular|0KA4S8R39M]].\n\n## Remarks\n\nIts shortest cycle has length $5$. It is not [[Hamiltonian|090WPKFABX]], and it is not [[planar|029JQEK15B]].\nIts [[chromatic number|0C5M7AM6FH]] is $3$, and its edges cannot be coloured with $3$ colours.\nA common drawing shows it as a pentagon outside, a pentagram inside, and five spokes.\n\n## Explanations\n\n### L1 human\n\nThe Petersen graph is a small graph with $10$ vertices and $15$ edges.\nIt is a standard counterexample: many statements that seem true for all cubic graphs fail for it.\n",
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