Shadow chains and Conley chains for continuous-time semiflows

Abstract

In a recent series of articles we introduced the concept of "stream of a semiflow. A stream is a closed and transitive binary relation which extends the relation "being on the orbit of" and allows to encode the qualitative behavior of a semiflow into a direct graph. The most important stream of a semiflow is its chain stream, based on Charles Conley's chains. In those previous works we omitted several details and proofs on continuous-time semiflows. In the present work we complement those articles as follows: (i) we provide a full proof of the closedness and transitivity of the chain stream for continuous-time semiflows; (ii) we introduce the concept of ``shadow chain'' for a continuous-time semiflow, based on the Anosov-Sinai-Bowen idea of pseudo-orbit. Shadow chains have the advantage that fit naturally with semiflows arising from differential equations. Our main result is that, although the shadow chain stream and the Conley chain stream are in general distinct as binary relations, they yield the same chain-recurrent set, the same nodes, and the same chain graph whenever the semiflow has strong compact dynamics. While doing this, we also introduce an equivalent definition of recurrent point of a stream in terms of forward-orbit equivalence, which simplifies several arguments below, and we strengthen the definition of s-uniform continuity of a semiflow, fixing a gap in the proof of some important results when the space is not locally compact. This is a radical revision of the first version posted to the arXiv.