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The Nash-Williams–Tutte tree packing theorem and Nash-Williams' arboricity theorem

Juan Pablo Traverso Gianini

Palomar Registrypalomar/PALOMAR-2026-10-17-000008Oct 17, 2026math.COscore 0

A Lean 4 / Mathlib formalization of three classical results on edge-disjoint trees and forests in finite simple graphs, none of which is in Mathlib. (1) The Nash-Williams–Tutte tree packing theorem: a graph has k edge-disjoint spanning trees if and only if every partition of its vertices into m parts has at least k(m − 1) edges between different parts. (2) Nash-Williams' arboricity theorem: the edges can be covered by k forests if and only if every nonempty vertex set S spans at most k(|S| − 1) edges. (3) The corollary that every 2k-edge-connected graph has k edge-disjoint spanning trees.…

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