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A graph G is diameter-2-critical if its diameter is 2, and the deletion of any edge strictly increases the diameter. The longstanding Murty–Simon Conjecture states that for any diameter-2-critical graph G of order n, e(G)≤⌊[Formula presented]⌋ and the unique extremal graph is K⌈n/2⌉,⌊n/2⌋. After more than ten years, Füredi (JGT,1992) confirmed the Murty–Simon Conjecture for sufficiently large n. In the same paper, Füredi claimed (without proof) that all diameter-2-critical graphs with at least ⌊[Formula presented]⌋+1 edges are complete bipartite graphs and M, where M is obtained by subdividing one edge of K⌈(n−1)/2⌉,⌊(n−1)/2⌋. Later, Balbuena, Hansberg, Haynes, and Henning (Graphs Combin., 2015) presented a class of diameter-2-critical graphs containing M. And all of them have ⌊[Formula presented]⌋+1 edges. So Füredi's claim needs to be revised. In this paper, we prove that all C5-free diameter-2-critical graphs with at least ⌊[Formula presented]⌋+1 edges are complete bipartite graphs for sufficiently large n. © 2025 Elsevier B.V.
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Discrete Applied Mathematics
ISSN: 0166-218X
Year: 2025
Volume: 375
Page: 332-337
1 . 0 0 0
JCR@2023
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