Past exam of the mathematics course of the University of Cambridge 2023 ii Paper 2 26G d Solution Created 2026-09-24 Updated 2026-10-03
No. For sufficiently smooth curves,is unchanged by proper Euclidean motions and transforms correctly under translations of the arc-length parameter, so it is a pointwise Euclidean invariant of a curve. It is not determined by the two numbers and .
For a concrete comparison near , use the plane curve reconstructed from curvature construction withThe resulting unit-speed planar curves both have and , but their curvature derivatives at zero are respectively and . Thus no single function can satisfy for all curves.
Indeed, the covariance conditions alone even permit nonlocal examples such as . This is the distinction recorded by pointwise Euclidean invariants need not depend only on current curvature and torsion.