@book{PPN592283712, title = {Ebene Trigonometrie Bd. 2, Abth. 1}, series = {GDML\_Books}, publisher = {Hahn}, year = {1876}, language = {de}, url = {http://dml.mathdoc.fr/item/PPN592283712} }
Wittstein, Theodor. Ebene Trigonometrie Bd. 2, Abth. 1. GDML_Books (1876), http://gdmltest.u-ga.fr/item/PPN592283712/