Liu, Qing, and Xiaodan Zhou. “Horizontal Convex Envelope in the Heisenberg Group and Applications to Sub-Elliptic Equations”. ANNALI SCUOLA NORMALE SUPERIORE - CLASSE DI SCIENZE 22, no. 4 (December 22, 2021): 2039-2076. Accessed May 26, 2026. https://journals-dev.sns.it/index.php/annaliscienze/article/view/886.