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Answers for “为什么三女两男的例子证明不可能有匹配?”

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Hall's theorem is introduced as the converse of the Bottleneck Lemma: if there are no bottlenecks in the bipartite graph, then there is a match. The video explicitly notes that this direction is not obvious and will be discussed next.

Conditions: Applies to bipartite graphs.; Requires the condition of having no bottlenecks.

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E(S)E(S) denotes the neighborhood of a subset S of the left-side vertices in the right-side set. It is the set of all right-side vertices adjacent to at least one vertex in S.

Conditions: S is a subset of the left-side vertices.; Adjacency is taken in the given bipartite graph.

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The converse of Hall's Theorem states that if a bipartite graph has no bottlenecks, then it must contain a perfect matching. The presenter notes that this result is not immediately obvious and indicates that the proof will follow in the next section.

Conditions: Applies to bipartite graphs.; Requires the condition of having no bottlenecks.

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The Bottleneck Lemma states that if a bipartite graph has a bottleneck, then no perfect matching exists. This is considered obvious from the counting argument.

Conditions: There is a subset S of the left-side vertices.; |S| > |E(S)E(S)|.