@article{SM_1981_40_4_a0,
     author = {L. I. Gal'chuk},
     title = {Optional martingales},
     journal = {Sbornik. Mathematics},
     pages = {435--468},
     year = {1981},
     volume = {40},
     number = {4},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1981_40_4_a0/}
}