@article{10_4064_aa_91_1_43_55,
     author = {Ulrike Vorhauer and Eduard Wirsing},
     title = {Three two-dimensional {Weyl} steps in the circle problem {I.} {The} {Hessian} determinant},
     journal = {Acta Arithmetica},
     pages = {43--55},
     publisher = {mathdoc},
     volume = {91},
     number = {1},
     year = {1999},
     doi = {10.4064/aa-91-1-43-55},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/aa-91-1-43-55/}
}