Litterature on "small" or "compact" dimensions? Hi! I'm reading some Kaluza-Klein theory which is an extension of normal 4D GR to a 5D spacetime in which the fifth dimension is a "small" or "compact" extra spatial dimension. I've found loads of literature on the differential geometry of hypersurfaces in higher-dimensional spaces, but I've not found anything on (the diff. geometry of) compact or small spaces. Does anyone have any recommendations on what to read in this regard? Thanks!