1. On the total curvature of immersed manifolds;Chern, Shiing-shen;Amer. J. Math.,1957
2. Critical submanifolds of the classical groups and Stiefel manifolds;Frankel, Theodore,1965
3. Minimal imbeddings of 𝑅-spaces;Takeuchi, Masaru;J. Differential Geometry,1968
4. Immersions with minimal total absolute curvature;Kuiper, Nicolaas H.,1959
5. The existence of polar non-degenerate functions on differentiable manifolds;Morse, Marston;Ann. of Math. (2),1960