On D sot hat x2-Dy2 represents m and -m and not -1.
Robertson, John P.
Acta Mathematica Academiae Paedagogicae Nyí regyháziensis. New Series [electronic only], Tome 26 (2009), p. 155-164 / Harvested from The Electronic Library of Mathematics
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Publié le : 2009-01-01
EUDML-ID : urn:eudml:doc:232531 
@article{05854976,
     title = {On },
     journal = {Acta Mathematica Academiae Paedagogicae Ny\'\i\ regyh\'aziensis. New Series [electronic only]},
     volume = {26},
     year = {2009},
     pages = {155-164},
     zbl = {1224.11050},
     language = {en},
     url = {http://dml.mathdoc.fr/item/05854976}
}

Robertson, John P. On . Acta Mathematica Academiae Paedagogicae Nyí regyháziensis. New Series [electronic only], Tome 26 (2009) pp. 155-164. http://gdmltest.u-ga.fr/item/05854976/