@article{SM_2014_205_5_a3,
     author = {E. S. Zaputryaeva},
     title = {Isometric deformations of planar quadrilaterals with constant index},
     journal = {Sbornik. Mathematics},
     pages = {663--683},
     publisher = {mathdoc},
     volume = {205},
     number = {5},
     year = {2014},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_2014_205_5_a3/}
}