Functional analysis of the backed tools coming from the Gravettian layers 23 and 22 of Paglicci Cave (Foggia, Italy) - Borgia, Valentina ('Prehistoric technology'. 40 years later: functional studies and the Russian legacy. Wear-traces, ethnoarchaeology, experimental archaeology. Proceedings of the international congress, Verona (Italy), 20-23 april 2005., 2008)