H1/2 maps with values into the circle : minimal connections, lifting, and the Ginzburg–Landau equation Jean Bourgain, Haim Brezis, Petru Mironescu (2004) Publications Mathématiques de l'IHÉS
Hamiltoniens quasi-convexes quasi-concaves M. Atteia, A. Elqortobi (1991) RAIRO - Operations Research - Recherche Opérationnelle