@article{IM2_1990_35_3_a4,
     author = {A. I. Degtyarev},
     title = {Classification of surfaces of degree four having a~nonsimple singular point},
     journal = {Izvestiya. Mathematics },
     pages = {607--627},
     publisher = {mathdoc},
     volume = {35},
     number = {3},
     year = {1990},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1990_35_3_a4/}
}