@article{JGG_2020_24_1_JGG_2020_24_1_a2,
     author = {H. Katsuura },
     title = {Solid {Angle} {Sum} of a {Tetrahedron}},
     journal = {Journal for geometry and graphics},
     pages = {29--34},
     publisher = {mathdoc},
     volume = {24},
     number = {1},
     year = {2020},
     url = {http://geodesic.mathdoc.fr/item/JGG_2020_24_1_JGG_2020_24_1_a2/}
}