An **unfriendly partition** is a concept that arises in the context of graph theory and combinatorics. Generally, it refers to a way of partitioning a set of elements, such as vertices in a graph, where certain pairs of elements have a restricted relationship (e.g., they cannot be grouped together in the same subset) due to specific constraints.
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An unfriendly partition puts at least as many neighbours of every vertex in the opposite part as in its own part.