Fractional covering conjecture for looms

Let AA and BB be hypergraphs forming an (r,s)(r,s)-loom, and write L=(A,B)\mathbb{L}=(A,B). Define the fractional covering number of the loom by

τ(L)=τ(AB).\tau^*(\mathbb{L})=\tau^*(A\cup B).

Here τ\tau^* is the minimum total weight of a nonnegative fractional vertex cover.

Loom fractional covering conjecture. If L=(A,B)\mathbb{L}=(A,B) is an (r,s)(r,s)-loom, then

τ(L)=max(r,s).\tau^*(\mathbb{L})=\max(r,s).

The source has the upper bound τ(L)max(r,s)\tau^*(\mathbb{L})\leqslant\max(r,s) and proposes equality; it also notes that this conjecture would imply the Gyárfás–Lehel conjecture in the equal-uniformity setting. It remains open.

Sources & referencesView supporting material

Primary source

Ron Aharoni, Eli Berger, Joseph Briggs, He Guo and Shira Zerbib, “Looms”, arXiv:2309.03735 (2024).

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