@article{oai:tsukuba.repo.nii.ac.jp:00016290,
 author = {Iwashita, Hirokazu},
 issue = {2},
 journal = {Tsukuba Journal of Mathematics},
 month = {Dec},
 pages = {241--256},
 title = {Spectral theory for symmetric systems in an exterior domain},
 volume = {11},
 year = {1987}
}