@misc{Natanson_Władysław_(1864-1937)_Theorems_1930,
 author={Natanson, Władysław (1864-1937)},
 address={Cracovie},
 howpublished={online},
 year={1930},
 publisher={Imprimerie de l'Université},
 language={eng},
 type={text},
 title={Theorems connected with Fermat's principle},
 keywords={zasada Fermata, optyka geometryczna},
}