Past exam of the mathematics course of the University of Cambridge 2024 iii Paper 202 5 c i Solution Created 2026-09-24 Updated 2026-09-25
The assertion is false. For a common sequence, each term of which is a refining deterministic partition of an interval, standard Brownian paths have quadratic variation almost surely, whereas the paths have quadratic variation almost surely. These two path properties define disjoint measurable subsets of , so the two laws are mutually singular measures. In particular, the law of is not absolutely continuous with respect to Wiener measure. This is the Pathwise quadratic variation distinguishes Brownian speeds argument.