@misc{Spencer_William_George_Inventional_1880,
 author={Spencer, William George},
 editor={Spencer, Herbert (1820–1903). Wstęp},
 copyright={Public Domain},
 address={London},
 howpublished={online},
 year={1880},
 publisher={Walter Smith},
 language={eng},
 language={eng},
 type={Text},
 title={Inventional geometry : a series of problems, intended to familiarize the pupil with geometrical conceptions, and to exercise his inventive faculty},
 URL={http://www.rcin.org.pl/impan/Content/32924/PDF/WA35_51189_5676_Inventional.pdf},
}