@article{JMPA_1861_2_6__225_0,
     author = {Liouville, J.},
     title = {Sur les deux formes quadratiques $x^2+y^2+z^2+2t^2$, $x^2+2\left(y^2+z^2+t^2\right)$},
     journal = {Journal de Math\'ematiques Pures et Appliqu\'ees},
     pages = {225--230},
     publisher = {Gauthier-Villars},
     volume = {2e s{\'e}rie, 6},
     year = {1861},
     language = {fr},
     url = {http://www.numdam.org/item/JMPA_1861_2_6__225_0/}
}