Claims

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2013_06_04_house: House (Discrete Math. 2013) proves that the smallest number of edges of a graph of dimension four is nine and that K_{3,3} is the only graph without isolated vertices attaining it, the first proof of the value; accepted.

2016_02_01_chaffee_noble: Theorem 6 of Chaffee and Noble (Australas. J. Combin. 2016) proves that the minimum number of edges of a graph of dimension four is nine, with Lemma 3 supplying K_{3,3} as the witness and Theorem 7 its uniqueness; accepted.

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