A generalization of Steiner symmetrization for immersed surfaces and its applications

We generalize the classical Steiner symmetrization to surfaces with self-intersections. Then we apply the generalized Steiner symmetrization to several isoperimetric problems. For example, let G{cyrillic}⊂ℝ³ be an analytic plane Jordan curve which is symmetric with respect to a plane π{variant} (π{variant}⊅G{cyrillic}). Let S be a compact immersed surface bounded by Λ which has the smallest area among all compact surfaces bounded by Λ with a fixed volume. In this situation, under some additional assumptions, the whole S is proved to be symmetric with respect to π{variant}. When Λ is a round circle, S is proved to be a spherical cap or the flat disk bounded by Λ without any additional assumptions.