Density of $C_{-4}$-critical signed graphs

Reza Naserasr, Lan Anh Pham, Zhouningxin Wang

A signed bipartite (simple) graph $(G,\sigma )$ is said to be $C_{-4}$-critical if it admits no homomorphism to $C_{-4}$ (a negative 4-cycle) but every proper subgraph of it does. In th…