@article{10_21136_CMJ_1991_102452,
     author = {Bart\'ak, Jaroslav and Vejvoda, Otto},
     title = {Periodic solutions to linear partial differential equations of the first order},
     journal = {Czechoslovak Mathematical Journal},
     pages = {185--202},
     publisher = {mathdoc},
     volume = {41},
     number = {2},
     year = {1991},
     doi = {10.21136/CMJ.1991.102452},
     mrnumber = {1105435},
     zbl = {0778.35005},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/CMJ.1991.102452/}
}