1. Athanassenas M.: A variational problem for constant mean curvature surfaces with free boundary. J. für Math. 377, 97–107 (1987)
2. Beer A: Tractatus de Theoria Mathematica Phenomenorum in Liquidis Actioni Gravitatis Detractis Observatorum. George Carol, Bonn (1857)
3. Bolza O: Lectures on the Calculus of Variations. University of Chicago Press, Chicago (1904)
4. Courant R., Hilbert D.: Methods of Mathematical Physics. Wiley, New York (1989)
5. Delaunay C.E.: Sur la surface de révolution dont la courbure moyenne est constante. J. Math. Pure et App. 16, 309–315 (1841)