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  "body": "\n## Summary\n\nA graph $H$ is a minor of a graph $G$ if $H$ can be obtained from $G$ by deleting vertices, deleting edges and contracting edges.\nThe minor relation is a partial order on finite graphs up to isomorphism.\nMany natural classes, such as planar graphs and forests, are closed under taking minors.\n[[Wagner's theorem|1B2ZJPVV03]] describes planar graphs by two forbidden minors, and the [[Robertson–Seymour theorem|WP3GDNWJJW]] shows that every minor-closed class has a finite list of forbidden minors.\n\n## Explanations\n\n### L1 human\n\nTake a graph and allow three moves: erase a vertex, erase an edge, or shrink an edge so that its two ends merge into one vertex.\nAny graph you can reach this way is a minor of the original.\nFor example, shrinking the five spokes of the Petersen graph turns it into the complete graph $K_5$.\nMinors capture the idea of one graph being hidden inside another in a coarse, flexible way.\n",
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