@misc{Joel_M._II.,
 author={Joel, M.},
 address={[S.l.]},
 howpublished={online},
 publisher={[s.n.]},
 language={ger},
 title={II. Oberschlesien : deutsche Zeit um 1350},
 keywords={historia, Śląsk Górny, kartografia, mapy, średniowiecze},
}