A(n attempt of a) systematic exposition of the basics of a Fibrational Theory of Geometric Morphisms based essentially on the work of B'enabou, Moens et. al. can be found in the diploma thesis of my student Peter Lietz under the www-address http://www.mathematik.tu-darmstadt.de/ags/ag14/mitglieder/lietz-de.html A new aspect seems to be that Moens' characterisation of geometricity of a fibration is essentially extensivity of the fibred category albeit w.r.t. internal sums. Thomas Streicher