@article{JGG_2019_23_2_JGG_2019_23_2_a3,
     author = {H. Katsuura},
     title = {Three-Dimensional {Viviani} {Theorem} on a {Tetrahedron}},
     journal = {Journal for geometry and graphics},
     pages = {179--182},
     year = {2019},
     volume = {23},
     number = {2},
     url = {http://geodesic.mathdoc.fr/item/JGG_2019_23_2_JGG_2019_23_2_a3/}
}