Constantin, Adrian, and Boris Kolev. “Geodesic Flow on the Diffeomorphism Group of the Circle”. Commentarii Mathematici Helvetici, vol. 78, no. 4, 2003, pp. 787-04, https://doi.org/10.1007/s00014-003-0785-6.
Constantin, A., & Kolev, B. (2003). Geodesic flow on the diffeomorphism group of the circle. Commentarii Mathematici Helvetici, 78(4), 787-804. https://doi.org/10.1007/s00014-003-0785-6
Constantin A, Kolev B. Geodesic flow on the diffeomorphism group of the circle. Commentarii Mathematici Helvetici. 2003;78(4):787-804.