Vincenzo Ciancia Gian Luigi Ferrari Co-Algebraic Models for Quantitative Spatial Logics. 43-58 2007 190 Electr. Notes Theor. Comput. Sci. 3 http://dx.doi.org/10.1016/j.entcs.2007.07.004 db/journals/entcs/entcs190.html#CianciaF07