@article{MZM_1994_56_1_a0,
     author = {A. P. Gurevich and A. P. Khromov},
     title = {First and second order differentiation operators with weight functions of variable sign},
     journal = {Matemati\v{c}eskie zametki},
     pages = {3--15},
     publisher = {mathdoc},
     volume = {56},
     number = {1},
     year = {1994},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1994_56_1_a0/}
}