@article{DAN_1967_174_2_a9,
     author = {P. E. Sobolevskii},
     title = {Comparison theorem for fractional powers of operators},
     journal = {Doklady Akademii Nauk},
     pages = {294--297},
     publisher = {mathdoc},
     volume = {174},
     number = {2},
     year = {1967},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1967_174_2_a9/}
}