@article{VM_2003_5_4_a1,
     author = {Paulus Gerdes},
     title = {Oblique altitudes and bisectors},
     journal = {Visual Mathematics},
     publisher = {mathdoc},
     volume = {5},
     number = {4},
     year = {2003},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/VM_2003_5_4_a1/}
}