@article{oai:tsukuba.repo.nii.ac.jp:00029687,
 author = {Okayasu, Takashi},
 issue = {2},
 journal = {Tsukuba Journal of Mathematics},
 month = {Dec},
 pages = {539--542},
 title = {A gap theorem for complete four-dimensional manifolds with δW^+ = 0},
 volume = {29},
 year = {2005}
}