Transactions on Combinatorics (Sep 2018)
Sufficient conditions for triangle-free graphs to be super-$λ'$
Abstract
An edge-cut $F$ of a connected graph $G$ is called a restricted edge-cut if $G-F$ contains no isolated vertices. The minimum cardinality of all restricted edge-cuts is called the restricted edge-connectivity $λ'(G)$ of $G$. A graph $G$ is said to be $λ'$-optimal if $λ'(G)=\xi(G)$, where $\xi(G)$ is the minimum edge-degree of $G$. A graph is said to be super-$λ'$ if every minimum restricted edge-cut isolates an edge. In this paper, first, we provide a short proof of a previous theorem about the sufficient condition for $λ'$-optimality in triangle-free graphs, which was given in [J. Yuan and A. Liu, Sufficient conditions for $λ_k$-optimality in triangle-free graphs, Discrete Math., 310 (2010) 981--987]. Second, we generalize a known result about the sufficient condition for triangle-free graphs being super-$λ'$ which was given by Shang et al. in [L. Shang and H. P. Zhang, Sufficient conditions for graphs to be $λ'$-optimal and super-$λ'$, Network}, 309 (2009) 3336--3345].
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