  A real photon has a complicated nature, whereby it may remain unresolved or
fluctuate into a vector meson or a perturbative q-qbar pair. Based on this
picture, we previously presented a model for gamma-p events that is based on
the presence of three main event classes: direct, VMD and anomalous. In
gamma-gamma events, a natural generalization gives three-by-three combinations
of the nature of the two incoming photons, and thus six distinct event classes.
The properties of these classes are constrained by the choices already made, in
the gamma-p model, of cut-off procedures and other aspects. It is therefore
possible to predict the energy-dependence of the cross section for each of the
six components separately. The total cross section thus obtained is in good
agreement with data, and also gives support to the idea that a simple
factorized ansatz with a pomeron and a reggeon term can be a good
approximation. Event properties undergo a logical evolution from p-p to gamma-p
to gamma-gamma events, with larger charged multiplicity, more transverse energy
flow and a higher jet rate in the latter process.
