Pinamonti, Andrea, och Enrico Valdinoci. ”A Geometric Inequality for Stable Solutions of Semilinear Elliptic Problems in the Engel Group”. Annales Fennici Mathematici 37, no. 2 (augusti 1, 2012): 357–373. åtkomstdatum maj 20, 2024. https://afm.journal.fi/article/view/135401.