@article{ELMA_1968__23_140890,
     author = {Josef P. Tschupik},
     title = {\"Uber {Drehfl\"achenumrisse} in {Perspektive} und schiefer {Axonometrie.}},
     journal = {Elemente der Mathematik},
     pages = {73--78},
     publisher = {mathdoc},
     volume = {23},
     year = {1968},
     zbl = {0159.25601},
     url = {http://geodesic.mathdoc.fr/item/ELMA_1968__23_140890/}
}