An edge-critical graph is a graph for which deleting any graph edge lowers the chromatic
number. More specifically, a graph is
-edge-critical if its chromatic
number is
and
for every edge
(Jensen and Toft 1995, Chiu et al. 2024).
The complete graph is
-edge-critical, while the cycle
graph
is 3-edge-critical. The Chiu graph is a 4-edge-critical
quartic graph and a planar
graph.