# knot complement

I was told that a knot complement in $S^3$ is an Eilenberg-Mc Lane space. And that it is quite easy to see this. However I am not able to find out why. could you help? Thanks

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Papakyriakopoulos, C. D. On Dehn's lemma and the asphericity of knots. Ann. of Math. (2) 66 (1957), 1–26.

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