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In mathematics, two links L 0 ⊂ S n {\displaystyle L_{0}\subset S^{n}} and L 1 ⊂ S n {\displaystyle L_{1}\subset S^{n}} are concordant if there exists an embedding f : L 0 × → S n × {\displaystyle f:L_{0}\times \to S^{n}\times } such that f = L 0 × { 0 } {\displaystyle f=L_{0}\times \{0\}} and f = L 1 × { 1 } {\displaystyle f=L_{1}\times \{1\}}.
By its nature, link concordance is an equivalence relation. It is weaker than isotopy, and stronger than homotopy: isotopy implies concordance implies homotopy. A link is a slice link if it is concordant to the unlink.