@article{ERAAMS_2001_07_a6,
     author = {Lauter, Robert and Nistor, Victor},
     title = {On spectra of geometric operators on open manifolds and differentiable groupoids},
     journal = {Electronic research announcements of the American Mathematical Society},
     pages = {45--53},
     publisher = {mathdoc},
     volume = {07},
     year = {2001},
     doi = {10.1090/S1079-6762-01-00093-2},
     url = {http://geodesic.mathdoc.fr/articles/10.1090/S1079-6762-01-00093-2/}
}