@article{MARSLBB_1857__30_179043,
     author = {Liagre},
     title = {Probl\`eme des cr\'epuscules.},
     journal = {M\'emoires de l 'Acad\'emie Royale des Sciences, des Lettres et des Beaux-Arts de Belgique. Collection in 4},
     pages = {1--1},
     year = {1857},
     volume = {30},
     zbl = {11.0029.02},
     url = {http://geodesic.mathdoc.fr/item/MARSLBB_1857__30_179043/}
}