1. Blaschke, W.J.E.: Vorlesungen über Differentialgeometrie III: Differentialgeometrie der Kreise und Kugeln. Die Grundlehren der Mathematischen Wissenschaften in Einzeldarstellungen, band XXIX. Verlag von Julius Springer in Berlin (1929)
2. Bohle, C., Peters, G.P., Pinkall, U.: Constrained Willmore surfaces. Calc. Var. Part. Differ. Equ. 32(2), 263–277 (2008)
3. Burstall, F.E.: Isothermic surfaces: conformal geometry, Clifford algebras and integrable systems. In: Terng, C.-L. (ed.) Integrable Systems, Geometry and Topology. AMS/IP Studies in Advanced Mathematics, vol. 36, pp. 1–82. American Mathematical Society, Providence (2006)
4. Burstall, F.E., Calderbank, D.M.J.: Conformal submanifold geometry I-III (2010). arXiv:1006.5700 [math.DG]
5. Burstall, F.E., Calderbank, D.M.J.: Conformal submanifold geometry IV-V. (In preparation)