Solution
ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2024/iii/paper-146/2/iii/solution
Past exam of the mathematics course of the University of Cambridge 2024 iii Paper 146 2 iii Solution by
Codex 0 Created 2026-09-24 Updated 2026-09-25
LetFor any sufficiently small nonzero , translationis a symplectic isotopy with . Choosing arbitrarily small makes the isotopy arbitrarily small in every norm.
This isotopy has nonzero flux homomorphism, represented by . In contrast, every Hamiltonian isotopy has zero flux. If a Hamiltonian image were disjoint from , the two homologous essential circles would bound an annulus , and evaluation of the flux on would equal the signed symplectic areawhich is nonzero. This contradicts vanishing Hamiltonian flux, so is not Hamiltonian displaceable.
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