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  "body": "\n## Summary\n\nA framework is a [[graph|00C0BR7D7H]] whose vertices are placed at points of Euclidean space, with the edges read as rigid bars joined at the vertices.\nThe framework is rigid when it cannot be deformed a little without changing some bar length, except by moving it as a whole.\nRigidity theory decides this from the graph and the positions, and in the plane [[Laman graphs|C81JPZ51NA]] answer the question for generic positions.\nIt belongs to [[distance geometry|HPW5F0GQ4B]] and has uses in engineering, robotics and molecular biology.\n\n## Explanations\n\n### L1 human\n\nBuild a shape from sticks joined by loose hinges at the ends.\nA triangle of sticks holds its shape: three side lengths fix the triangle.\nA square of four sticks does not: you can push it over into a rhombus while every stick keeps its length.\nAdding one diagonal stick to the square makes it rigid again.\nRigidity theory asks which stick figures behave like the triangle and which like the square.\n",
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