@article{oai:tsukuba.repo.nii.ac.jp:00016142,
 author = {Shibata, Yoshihiro},
 issue = {2},
 journal = {Tsukuba Journal of Mathematics},
 month = {Dec},
 pages = {283--352},
 title = {On the Neumann problem for some linear hyperbolic systems of 2nd order with coeffcients in Sobolev spaces},
 volume = {13},
 year = {1989}
}