@article{MS2_1978__43_166599,
     author = {Henry W. Hansen},
     title = {On the {Gaussian} {Markoff} spectrum.},
     journal = {Mathematica Scandinavica},
     pages = {35--43},
     year = {1978},
     volume = {43},
     zbl = {0402.10031},
     url = {http://geodesic.mathdoc.fr/item/MS2_1978__43_166599/}
}