@article{SM_2004_195_9_a5,
     author = {A. Yu. Savin and B. Yu. Sternin},
     title = {Defect of index in the theory of non-local problems and the $\eta$-invariant},
     journal = {Sbornik. Mathematics},
     pages = {1321--1358},
     publisher = {mathdoc},
     volume = {195},
     number = {9},
     year = {2004},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_2004_195_9_a5/}
}