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
Homoclinic solutions for linear and linearizable ordinary differential equations. Avramescu, Cezar, Vladimirescu, Cristian (2000) Abstract and Applied Analysis