Combining the risk assumption with <Cramér-Rao bound> gives $(1+b')^2\le\gamma-Ib^2$. Taking the branch compatible with super-efficiency yields $b'\le-[1-\sqrt{\gamma-Ib^2}]\le-(1-\sqrt\gamma)$, equivalent to the displayed sharper pointwise inequality.

Solution

Past exam of the mathematics course of the University of Cambridge / 2026 / ii / Paper 4 / 28L / c / Solution

 Solution (source code)