Unitarity, analyticity and the relativistic three body problem

Some approaches are briefly discussed to the problem of unitarising the isobar model (i.e. finding satisfactory phisub(i)'s). It turns out that, in trying to solve the unitarisation problem in the cheapest way consistent with analyticity one is led to a simple model for the relativistic three body problem - one in fact, that generalises the old Khuri-Treiman model. Thus, the discussion is placed in the context of a search for good relativistic three particle equations. The necessity of having to attend to analyticity and unitarity, and the difficulty of doing do in a completely satisfactory way are emphasized. (Auth.)