@article{IM2_1978_12_3_a1,
     author = {A. B. Venkov},
     title = {Selberg's trace formula for the {Hecke} operator generated by an involution, and the eigenvalues of the {Laplace--Beltrami} operator on the fundamental domain of the modular group~$PSL(2,\mathbf Z)$},
     journal = {Izvestiya. Mathematics },
     pages = {448--462},
     publisher = {mathdoc},
     volume = {12},
     number = {3},
     year = {1978},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1978_12_3_a1/}
}