@article{ZNSL_2001_280_a18,
     author = {O. R. Musin},
     title = {Curvature extrema and four-vertex-theorems for polygons and polyhedra},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {251--271},
     publisher = {mathdoc},
     volume = {280},
     year = {2001},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_2001_280_a18/}
}