Codimension one structurally stable chain classes

The well-known stability conjecture of Palis and Smale states that if a diffeomorphism is structurally stable, then the chain recurrent set is hyperbolic. It is natural to ask if this type of result is true for an individual chain class, that is, whether or not every structurally stable chain class is hyperbolic. Regarding the notion of structural stability, there is a subtle difference between the case of a whole system and the case of an individual chain class. The latter is more delicate and contains additional difficulties. In this paper we prove a result of this type for the latter, with an additional assumption of codimension 1. Precisely, let f be a diffeomorphism of a closed manifold M and let p be a hyperbolic periodic point of f of index 1 or dim M − 1. We prove if the chain class of p is structurally stable, then it is hyperbolic. Since the chain class of p is not assumed in advance to be locally maximal, and since the counterpart of it for the perturbation g is defined not canonically but indirectly through the continuation p_g of p, the proof is quite delicate.