Tangle structure trees II: trees of tangles and tangle-tree duality

Abstract

Tangle structure trees, introduced in [3], offer a unified data structure that displays all the tangles of a graph or data set together with certificates for the non-existence of any other tangles, either locally or overall. In this paper we apply tangle structure trees to derive new versions of the two fundamental tangle theorems: the tree-of-tangles theorem, and the tangle-tree duality theorem. We extend the tree-of-tangles theorem to $\mathcal F$-tangles that need not be profiles. When $\mathcal F$ consists of stars of separations, as it does in classical tangle-tree duality theorems, we show how to convert tangle structure trees that certify the non-existence of $\mathcal F$-tangles into tree-decompositions that certify this in the way known from graph tangles, as $S$-trees over~$\mathcal F$.