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  "body": "\n## Summary\n\nA subspace $A$ of a space $X$ is a deformation retract when $X$ can be deformed continuously onto $A$.\nAt the end of the deformation, the points of $A$ are back where they started.\nThen the inclusion of $A$ in $X$ is a [[homotopy equivalence|XZG6MTSWCN]], so $A$ and $X$ have the same homotopy invariants.\nDeformation retractions are the main tool for replacing a space by a simpler one of the same [[homotopy type|SK0ZJGWXDP]].\n\n## Explanations\n\n### L1 human\n\nPicture a thick object melting slowly onto a thin skeleton inside it, with the skeleton itself held in place.\nAt the end of the melting, everything lies on the skeleton.\nFor example, the plane without the origin melts onto the unit circle if each point moves along its ray towards the circle.\nSo the punctured plane and the circle have the same holes.\n",
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