# SAS

## Seminar

### Resolute sets and initial segment complexity

Seminar Room 1, Newton Institute

#### Abstract

Notions of triviality have been remarkably productive in algorithmic randomness,with $K$-triviality being the most notable. Of course, ever since the original characterization of Martin-Löf randomness by initial segment complexity, there has been a longstanding interplay between initial segment complexity and calibrations of randomness, as witnessed by concepts such as autocomplexity, and the like. In this talk I wish to discuss recent work with George Barmpalias on a triviality notion we call**resoluteness**. Resoluteness is defined in terms of computable shifts by is intimately related to a notion we call weak resoluteness where $A$ is weakly resolute iff for all computable orders $h$, $K(A\uparrow n) \ge^+ K(A\uparrow h(n)), $ for all $n$. It is not difficult to see that $K$-trivials have this property but it turns out that there are uncountablly many degrees which are completely $K$-resolute, and there are c.e. degrees also with this property. These degrees seem related to Lathrop-Lutz

**ultracompressible**degrees. Our investigations are only just beginning and I will report on our progress. Joint work with George Barmpalias.

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