@article{10_4064_ba61_2_3,
     author = {A. Schinzel},
     title = {On {Sums} of {Four} {Coprime} {Squares}},
     journal = {Bulletin of the Polish Academy of Sciences. Mathematics},
     pages = {109--111},
     publisher = {mathdoc},
     volume = {61},
     number = {2},
     year = {2013},
     doi = {10.4064/ba61-2-3},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/ba61-2-3/}
}