  We illustrate geometric scaling for the photon-proton cross section with a
very simple saturation model. We describe the proton structure function F2 at
small x in a wide kinematical range with an elementary functional form and a
small number of free parameters. We speculate that the symmetry between low and
high Q2 recently discovered in the data could be related to a well-known
symmetry of the two-gluon- exchange dipole-dipole cross section.
