ISI/FSI in Threshold Meson Production - Onshell Approach and Coulomb   Problem
  The onshell description of Initial- and Final-State-Interactions (ISI and FSI) of threshold meson production reactions is reviewed. Existing onshell models and their offshell extension are discussed. Unitarity constraints on enhancement factors are formulated. A strategy for the treatment of essential singularities connected to Coulomb-like FSI is given. 
F. Kleefeld (CFIF, IST, Lisbon, Portugal)