@article{MAT_1974_18_6_a1,
     author = {G. Harder},
     title = {A {Gauss--Bonnet} formula for discrete arithmetically defined groups},
     journal = {Matematika},
     pages = {20--55},
     publisher = {mathdoc},
     volume = {18},
     number = {6},
     year = {1974},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MAT_1974_18_6_a1/}
}