@article{UFA_2011_3_1_a0,
     author = {K. P. Isaev and R. S. Yulmukhametov},
     title = {Unconditional exponential bases in {Hilbert} spaces},
     journal = {Ufa mathematical journal},
     pages = {3--15},
     publisher = {mathdoc},
     volume = {3},
     number = {1},
     year = {2011},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/UFA_2011_3_1_a0/}
}