Tung, Chia-chi, and Pier Domenico Lamberti. “On Rellich’s Lemma, the Poincaré Inequality, and Friedrichs Extension of an Operator on Complex Spaces”. CUBO, A Mathematical Journal 23, no. 2 (August 1, 2021): 265–285. Accessed January 19, 2022. https://revistas.ufro.cl/ojs/index.php/cubo/article/view/2716.