@article{JRAM_1927__157_149619,
     author = {G.H. Hardy and J.E. Littlewood},
     title = {Elementary theorems concerning power series with positive coefficients and moment constants of positive functions.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {141--158},
     publisher = {mathdoc},
     volume = {157},
     year = {1927},
     zbl = {53.0193.03},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1927__157_149619/}
}