Lipschitz magnitude conjecture for tractable subspaces

Let L1L_1 be the space of integrable real-valued functions with its usual metric, and let TL1T\subseteq L_1 be a tractable subspace. Write Fin+(T)\mathrm{Fin}_{+}(T) and Cmp+(T)\mathrm{Cmp}_{+}(T) for the spaces of finite and compact subspaces of TT, respectively, and let magFin+(T)\mathsf{mag}_{\mathrm{Fin}_{+}(T)} and magCmp+(T)\mathsf{mag}_{\mathrm{Cmp}_{+}(T)} denote their magnitude maps. A map is Lipschitz if there is a constant C0C\geq 0 such that its output differences are at most CC times the distances between inputs.

Lipschitz magnitude conjecture. Let TL1T\subseteq L_1 be tractable. Then

magCmp+(T) ⁣:Cmp+(T)R\mathsf{mag}_{\mathrm{Cmp}_{+}(T)}\colon \mathrm{Cmp}_{+}(T)\to\mathbb{R}

is Lipschitz if and only if TT is bounded. Equivalently, the magnitude map on Fin+(T)\mathrm{Fin}_{+}(T) is Lipschitz if and only if TT is bounded; for tractable TT, boundedness is equivalent to compactness.

This conjecture characterizes exactly when magnitude has global Lipschitz continuity on compact or finite subspaces of a tractable subspace of L1L_1.

Sources & referencesView supporting material

Primary source

Sara Kališnik and Davorin Lešnik, “Tractable Metric Spaces and Magnitude Continuity”, arXiv:2506.21128 (2026).

Additional references

2 papers in this index state this conjecture (2019–2025). The statement above is taken from the most recent of them; the others are arXiv:1904.08923.

Progress summary

Never refreshed

Nothing recorded yet. Refresh searches the literature and the public web for attempts on this problem, and writes the first summary here.

Solutions 0

No solutions have been posted yet.