@article{10_4064_ap_21_2_223_230,
     author = {L. V. Toralballa},
     title = {Piecewise flatness and surface area},
     journal = {Annales Polonici Mathematici},
     pages = {223--230},
     publisher = {mathdoc},
     volume = {21},
     number = {2},
     year = {1968},
     doi = {10.4064/ap-21-2-223-230},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/ap-21-2-223-230/}
}