@book{PPN593043049, title = {Die ebene Trigonometrie Band 3}, series = {GDML\_Books}, publisher = {Hahn}, year = {1864}, language = {de}, url = {http://dml.mathdoc.fr/item/PPN593043049} }
Helmes, Joseph. Die ebene Trigonometrie Band 3. GDML_Books (1864), http://gdmltest.u-ga.fr/item/PPN593043049/