Past exam of the mathematics course of the University of Cambridge 2014 iii Paper 30 4 Solution Created 2026-10-03 Updated 2026-10-06
Let . For any , the setis compact. If it is empty there is nothing to prove. Otherwise continuity and the unique minimum give a strictly positive separation gapTake any measurable attained minimizer of . Its defining inequality givesConsequentlyThis proves argmin consistency under uniform convergence in probability. No continuity of is needed once the minimizer exists; compactness and continuity concern the deterministic separation gap. The uniform convergence in probability assumption controls all candidate parameters, including the random minimizer.
For the estimating equation, fix and put , . The prescribed signs make . Pointwise convergence in probability at just these two points impliesand similarly . With probability tending to one, . The intermediate value theorem then gives a zero inside , and uniqueness identifies it with . HenceThis is consistency of a uniquely bracketed zero. It needs no monotonicity, no continuity of the limit , and no uniform convergence of the . The bracket interval must lie in the domain of : read literally, the printed sign condition for every positive puts every real point into , so this requirement is satisfied. More generally it is enough to have an interval about and sign brackets arbitrarily close to it.