Past exam of the mathematics course of the University of Cambridge 2025 iii Paper 144 2 c iii Solution Created 2026-09-24 Updated 2026-09-24
Yes. Choose a nonprincipal ultrafilter on and letFor each fixed positive integer , the equality holds in the th factor exactly when divides . Only finitely many positive integers divide , so the cofinite set of indices for which belongs to . Łoś theorem gives in for every . Thus has infinite order of a group element.