@article{MV_1977_29_1_a31,
     author = {I. E. Sharkawi},
     title = {Boundary value problems for linear differential equations of operators},
     journal = {Matemati\v{c}ki vesnik},
     pages = {279 },
     year = {1977},
     volume = {29},
     number = {1},
     url = {http://geodesic.mathdoc.fr/item/MV_1977_29_1_a31/}
}