Multi-separation star refinement conjecture

About 11 years old · traced to

Let (U⃗,≤,∗,∨,∧)(\vec{U},\leq,*,\vee,\wedge) be a distributive universe of separations with an order function, and let {x←i:i∈[n]}\{\overleftarrow{x}_i:i\in[n]\} be a set of separations in U⃗\vec{U}. A set of separations is a star if its oriented separations point pairwise towards one another in the standard sense, and u⃗i\vec{u}_i is linked to x⃗i\vec{x}_i when the two separations satisfy the linking relation used in the preceding lemma.

Multi-separation star refinement conjecture. There exists a set of separations {u←i:i∈[n]}\{\overleftarrow{u}_i:i\in[n]\} such that:

  • {u←i:i∈[n]}\{\overleftarrow{u}_i:i\in[n]\} is a star;
  • u⃗i\vec{u}_i is linked to x⃗i\vec{x}_i for all i∈[n]i\in[n];
  • ∣u←i∣≤∣x←i∣|\overleftarrow{u}_i|\leq|\overleftarrow{x}_i| for all i∈[n]i\in[n];
  • u←i=x←i⋀j≠iu⃗j\overleftarrow{u}_i=\overleftarrow{x}_i\bigwedge_{j\neq i}\vec{u}_j for all i∈[n]i\in[n].

This would extend the preceding two-separation lemma to an arbitrary finite set of separations. The text calls it tempting rather than established, and no proof or resolution is supplied here.

References

Primary source

Joshua Erde, “Refining a Tree-Decomposition which Distinguishes Tangles”, arXiv:1512.02499 (2017).

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