Solution

ID: past-exam-of-the-year-1-of-the-computer-science-course-of-the-university-of-oxford/2022/discrete-mathematics-continuous-mathematics-and-probability/discrete-mathematics/3/b/solution

For a counterexample to closure under union of antisymmetric relations, take , , and . Each is an antisymmetric relation: neither contains an off-diagonal pair together with its reverse. But contains both and while . Therefore is not an antisymmetric relation.

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