References   Treccani.itTreccani.it: Enciclopedia, Vocabolario
(voce: Dimensionale, analisi); EMKEncyclopaedia of mathematics. An updated and annotated translation of the Soviet mathematical encyclopaedia, managing editor Michiel Hazewinkel, ed. in 6 v., Dordrecht [etc.], Kluwer academic publishers, 1995 + Supplement 1-3, 1997-2001.
; Wikipedia(IT)Wikipedia. L'enciclopedia libera, 2001 [ed. in lingua italiana dell' enciclopedia online Wikipedia]