@article{10_4064_aa158_1_5,
     author = {Kenneth S. Williams},
     title = {Quadratic forms and a product-to-sum formula},
     journal = {Acta Arithmetica},
     pages = {79--97},
     year = {2013},
     volume = {158},
     number = {1},
     doi = {10.4064/aa158-1-5},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/aa158-1-5/}
}