The 1-2-3 Conjecture for Borel Combinatorics

Abstract

The 1-2-3 Conjecture asserts that every finite graph without isolated edges admits edge weights from $\{1,2,3\}$ such that the sum function forms a vertex coloring. We study its Borel analogue for locally finite Borel graphs without isolated edges, proving that five weights suffice in general and four suffice for regular graphs. We obtain three weights for acyclic graphs admitting a Borel selection of a nonempty finite set of ends from each component. We also obtain $μ$-measurable and Baire measurable vertex-coloring $3$-edge weightings from $3$-colorings of the same definability, under probability measure-preserving and Baire quasi-invariance conditions, respectively.