The 6-edge-connectivity conjecture for strongly connected modulo 3-orientations

A graph is \mathbb Z_3-connected if, for every function β:V(G)Z3\beta:V(G)\to\mathbb Z_3 satisfying vV(G)β(v)0(mod3)\sum_{v\in V(G)}\beta(v)\equiv 0\pmod{3}, there is an orientation DD of GG such that dD+(v)dD(v)β(v)(mod3)d_D^+(v)-d_D^-(v)\equiv\beta(v)\pmod{3} for every vV(G)v\in V(G). An orientation is strongly connected if, for every two vertices x,yV(G)x,y\in V(G), there is a directed path from xx to yy. A graph is S3\mathcal S_3-connected if, for every Z3\mathbb Z_3 boundary function β\beta, it has a strongly connected orientation DD satisfying dD+(v)dD(v)β(v)(mod3)d_D^+(v)-d_D^-(v)\equiv\beta(v)\pmod{3} for every vertex vv.

The 6-edge-connectivity conjecture. Every 6-edge-connected graph has a strongly connected modulo 33-orientation.

This conjecture strengthens the known result that every 6-edge-connected graph is Z3\mathbb Z_3-connected. It was proved for 8-edge-connected graphs by Lovász, Thomassen, Wu and Zhang, while the 6-edge-connected case is therefore no longer open.

Sources & referencesView supporting material

Primary source

Rui Guan, Chenglin Jiang, Hong-Jian Lai, Jiaao Li and Xinyuan Li, “Realizing degree sequences with S_3-connected graphs”, arXiv:2502.18100 (2025).

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