@article{BUMI_1998_8_1B_1_a9,
     author = {Parenti, Cesare and Parmeggiani, Alberto},
     title = {Some remarks on almost-positivity of $\psi\text{do}$'s},
     journal = {Bollettino della Unione matematica italiana},
     pages = {187--215},
     publisher = {mathdoc},
     volume = {Ser. 8, 1B},
     number = {1},
     year = {1998},
     zbl = {0908.35146},
     mrnumber = {370271},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/BUMI_1998_8_1B_1_a9/}
}