@article{PORMA_1981__40_4_115473,
     author = {Gupta, V.P.},
     title = {Functions with negative coefficients},
     journal = {Portugaliae mathematica},
     pages = {439--448},
     publisher = {mathdoc},
     volume = {40},
     number = {4},
     year = {1981},
     mrnumber = {0836107},
     zbl = {0585.30015},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PORMA_1981__40_4_115473/}
}