@article{PORMA_1970__29_3_115123,
     author = {Hardy, John},
     title = {A note on the representability of quaternary quadratic forms as sums of squares of two linear forms},
     journal = {Portugaliae mathematica},
     pages = {161--164},
     publisher = {mathdoc},
     volume = {29},
     number = {3},
     year = {1970},
     mrnumber = {0323711},
     zbl = {0218.10036},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PORMA_1970__29_3_115123/}
}