@article{JMPA_1861_2_6__440_0,
     author = {Liouville, J.},
     title = {Sur les deux formes $\mathrm{X}^2+\mathrm{Y}^2+\mathrm{Z}^2+4\mathrm{T}^2$, $\mathrm{X}^2+4\mathrm{Y}^2+4\mathrm{Z}^2+4\mathrm{T}^2$},
     journal = {Journal de Math\'ematiques Pures et Appliqu\'ees},
     pages = {440--448},
     publisher = {Gauthier-Villars},
     volume = {2e s{\'e}rie, 6},
     year = {1861},
     language = {fr},
     url = {http://www.numdam.org/item/JMPA_1861_2_6__440_0/}
}