Hajlasz, Piotr, and Armin Schikorra. “Lipschitz Homotopy and Density of Lipschitz Mappings in Sobolev Spaces”.
Annales Fennici Mathematici
39, no. 2 (August 1, 2014): 593–604. Accessed April 7, 2025. https://afm.journal.fi/article/view/135503.