@misc{geometric+classification+of+natural+physical+cavities,
    author = {Bielek, Boris i Bielek, Milan},
    title = {Geometric classification of natural physical cavities},
    journal = {Czasopismo Techniczne. Budownictwo},
    address = {Kraków},
    publisher = {<a href=\"http://www.wydawnictwo.pk.edu.pl/\" target=\"_blank\">Wydawnictwo PK</a>},
    date = {2012},
    number = {R. 109, Z. 3, 2-B}
}