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  "body": "\n## Example\n\nThe *Pappus configuration* is a [[configuration|Q2QFXPP9EE]] $(9_3)$ in the projective plane.\nTake distinct points $A, B, C$ on a line $g$ and distinct points $a, b, c$ on another line $h$, none of them on both lines.\nLet $X = Ab \\cap aB$, $Y = Ac \\cap aC$ and $Z = Bc \\cap bC$.\nBy [[Pappus's hexagon theorem|B6C3J2GJWP]], $X$, $Y$, $Z$ lie on a line, the Pappus line.\n\nIts $9$ points are $A, B, C, a, b, c, X, Y, Z$.\nIts $9$ lines are $g$, $h$, the six lines $Ab$, $aB$, $Ac$, $aC$, $Bc$, $bC$ and the Pappus line.\nCheck: each line has $3$ of the points, for instance $Ab$ contains $A$, $b$, $X$ and $Bc$ contains $B$, $c$, $Z$.\nEach point lies on $3$ lines.\nFor instance, $A$ lies on $g$, $Ab$, $Ac$, the point $b$ on $h$, $Ab$, $bC$, and $X$ on $Ab$, $aB$ and the Pappus line.\nIts incidence graph is the Pappus graph.\n\n## Explanations\n\n### L1 human\n\nPut three points on one line and three on another, and join them crosswise in pairs.\nThe three crossing points always land on a common line.\nThe finished picture has $9$ points and $9$ lines, with $3$ points on each line and $3$ lines through each point.\n",
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