@article{IM2_1975_9_1_a2,
     author = {A. N. Tyurin},
     title = {On an invariant of a~double of quadrics},
     journal = {Izvestiya. Mathematics},
     pages = {21--25},
     year = {1975},
     volume = {9},
     number = {1},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1975_9_1_a2/}
}