@article{PMIHES_1993__78__187_0,
     author = {Schwartz, Richard Evan},
     title = {Pappus's theorem and the modular group},
     journal = {Publications Math\'ematiques de l'IH\'ES},
     pages = {187--206},
     publisher = {Institut des Hautes \'Etudes Scientifiques},
     volume = {78},
     year = {1993},
     zbl = {0806.57004},
     language = {en},
     url = {http://www.numdam.org/item/PMIHES_1993__78__187_0/}
}