@misc{Petersen_Julius_(1839–1910)_Lehrbuch_1881,
 author={Petersen, Julius (1839–1910)},
 editor={Fischer-Benzon, Rudolph von (1839–1911). Transl.},
 copyright={Public Domain},
 address={Kopenhagen},
 howpublished={online},
 year={1881},
 publisher={Verlag von Andr. Fred. Höst & Sohn},
 language={ger},
 title={Lehrbuch der elementaren Planimetrie},
 type={Text},
 URL={http://rcin.org.pl/Content/21628/PDF/WA35_19754_7006_Lehrbuch.pdf},
}