The expression 'a ∪ b' represents the union of two sets, a and b, which consists of all elements that are in either set a, set b, or in both. This operation is fundamental in set theory, as it allows the combination of multiple sets into one, highlighting how elements can be shared or unique across different sets. Understanding the union operation also ties into other key concepts such as intersection and complement, as these operations help to define relationships between sets.
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