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  "body": "\n## Summary\n\nA continuous map is null-homotopic when it is [[homotopic|F2F143KQ2M]] to a constant map.\nNull-homotopic maps are the trivial maps of homotopy theory.\nFor example, a map $S^n \\to Y$ is null-homotopic exactly when it extends over the disk $D^{n+1}$.\n\n## Explanations\n\n### L1 human\n\nA map is null-homotopic when its image can be shrunk continuously to a single point inside the target.\nEvery map into a disk is null-homotopic.\nEvery loop in the plane is null-homotopic, but in the plane without the origin a loop that goes once around the origin is not.\nNull-homotopic maps carry no information about the holes of the target.\n",
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