@article{PMIHES_1993__78__187_0,
     author = {Richard Evan Schwartz},
     title = {Pappus's theorem and the modular group},
     journal = {Publications Math\'ematiques de l'IH\'ES},
     pages = {187--206},
     year = {1993},
     publisher = {Institut des Hautes \'Etudes Scientifiques},
     volume = {78},
     doi = {10.1007/BF02712918},
     zbl = {0806.57004},
     language = {en},
     url = {https://pmihes.centre-mersenne.org/articles/10.1007/BF02712918/}
}