Past exam of the mathematics course of the University of Cambridge 2012 ia Paper 4 2D i Solution Created 2026-09-24 Updated 2026-10-07
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.