  Existing data for large-$t$ $pp$ elastic-scattering differential
cross-sections are energy-independent and behave as $t^{-8}$. This has been
explained in terms of triple-gluon exchange, or alternatively through
triple-singlet exchange. A discussion is given of the problems raised by each
of these explanations, and of the possibility that at RHIC or LHC energies the
exchange of three BFKL pomerons might result in a rapid rise with energy.
