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  "body": "\n## Definition\n\nLet $A$ and $B$ be [[sets|0SJ3RX9TXA]].\nThe union of $A$ and $B$ is the set\n$$A \\cup B = \\{x \\mid x \\in A \\lor x \\in B\\}.$$\nSo an object $x$ is an [[element|0EZ758XE73]] of $A \\cup B$ when $x \\in A$ or $x \\in B$, or both.\n\n## Remarks\n\nExample: $\\{1, 2\\} \\cup \\{2, 3\\} = \\{1, 2, 3\\}$.\nUnion is commutative and associative, and $A \\cup \\varnothing = A$.\nThe union of an arbitrary family of sets is in [[union of a family of sets|05GK32H72H]].\n\n## Explanations\n\n### L1 human\n\nTo form $A \\cup B$, put the elements of $A$ and the elements of $B$ together in one set.\nAn element of both sets appears only one time.\n",
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