@article{ZNSL_2017_463_a13,
     author = {V. P. Il'in},
     title = {Two-level least squares methods in {Krylov} subspaces},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {224--239},
     year = {2017},
     volume = {463},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_2017_463_a13/}
}