Open issues on the structure of multiple interactions are outlined. An
improved model is summarized, with a new approach to correlated parton
densities in flavour, colour, longitudinal and transverse momenta, for both
hard-scattering partons and beam-remnant ones.Comment: LaTeX, 5 pages, submitted to the proceedings of the Workshop on
Physics at TeV Colliders, Les Houches, France, 26 May - 6 June 200
