Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2012/ia/paper-4/2d/i/solution

The intersection is always an equivalence relation. Both component relations contain , so is a reflexive relation. If , both relations relate to , and symmetry in each gives . If and , transitivity in each component gives both and , hence . This is the intersection of equivalence relations; the same argument works for any family of such relations.

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