Dvořák–Postle edge conjecture for C5C_5-critical graphs

For a graph HH, an HH-critical graph is a graph that admits no homomorphism to HH, while every proper subgraph does. Here C5C_5 denotes the cycle on five vertices, and e(G)=E(G)e(G)=|E(G)|, v(G)=V(G)v(G)=|V(G)|.

Dvořák–Postle conjecture. If GG is C5C_5-critical, then

e(G)14v(G)911.e(G)\geq\frac{14v(G)-9}{11}.

This conjecture concerns the density of graphs critical for homomorphisms to the five-cycle and is stated after a weaker proven bound in the source; no resolution is supplied here.

Sources & referencesView supporting material

Primary source

Benjamin Moore, “Sparse 4-critical graphs have low circular chromatic number”, arXiv:2007.15556 (2020).

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