Verein., 38: 248–260 Papakyriakopoulos, C. D. (1957), "On Dehn's Lemma and the Asphericity of Knots", Proc.
38: 248—260 Papakyriakopoulos, C. D. (1957), «On Dehn’s Lemma and the Asphericity of Knots», Proc.