Stable frames and weights

by Shelah. [Sh:839]

Part I: We would like to generalize imaginary elements, weight of ortp (a,M,N),{bold P}-weight, {bold P}-simple types, etc. from [Sh:c, Ch.III,V,section 4] to the context of good frames. This requires allowing the vocabulary to have predicates and function symbols of infinite arity, but it seemed that we do not suffer any real loss. Part II: Good frames were suggested in [Sh:h] as the (bare bones) right parallel among a.e.c. to superstable (among elementary classes). Here we consider (mu, lambda, kappa)-frames as candidates for being the right parallel to the class of |T|^+-saturated models of a stable theory (among elementary classes). A loss as compared to the superstable case is that going up by induction on cardinals is problematic (for cardinals of small cofinality). But this arises only when we try to lift. But this context we investigate the dimension. Part III: In the context of Part II, we consider the main gap problem for the parallel of somewhat saturated model; showing we are not worse than in the first order case.

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