@article{PORMA_1981__40_2_115447,
     author = {Ferreira, Jos\'e M.},
     title = {Nonnegative point spectrum for differential equations with infinite delays},
     journal = {Portugaliae mathematica},
     pages = {239--251},
     publisher = {mathdoc},
     volume = {40},
     number = {2},
     year = {1981},
     mrnumber = {0819888},
     zbl = {0584.34049},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PORMA_1981__40_2_115447/}
}