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  "body": "\n## Summary\n\nA slice knot is a [[knot|QYEAZTYGPT]] in the $3$-sphere that bounds a smoothly embedded disk in the $4$-ball.\nThe notion links knot theory with the topology of [[4-manifolds|8H58Q6YJCH]].\nSlice knots are exactly the knots concordant to the [[unknot|1TQ06R4Q66]], and they form the zero element of the knot concordance group.\nThere is also a topological version, with locally flat disks, and the two versions differ.\n\n## Explanations\n\n### L1 human\n\nView ordinary space as the boundary of a four-dimensional ball, as a circle is the boundary of a disk.\nA knot is slice if, with the help of the extra dimension, it bounds a disk without self-intersections.\nIn three dimensions only the unknot bounds such a disk, but in four dimensions many knots do.\nThe sum of a knot and its reversed mirror image is always slice.\nThe [[trefoil knot|VYTYSVHN4A]] is not slice.\n",
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