  Most hadronic event generators which can be used for simulating hadronic and
nuclear collisions up to the highest energies are quite similar in their
construction and in the underlying theoretical concepts. At energies, where
data from accelerator and collider experiments are available the models agree
rather well with each other and with the most important features of the data.
As soon as we compare the extrapolations of the models at higher energy we find
in spite of the similarities in the underlying theoretical concepts quite often
striking differences between the predictions of the models.
