Past exam of the mathematics course of the University of Cambridge 2026 iii Paper 112 2 d Solution Created 2026-09-24 Updated 2026-09-24
For the supplied Seifert matrix ,and the symmetric form has signature . ThusSince the Levine-Tristram signature is an additive homomorphism on the algebraic concordance group, has infinite algebraic-concordance order.
Over , reduction of the Alexander polynomial givesThe factors are coprime, nonsymmetric, and exchanged by reciprocity. Hensel lifting therefore decomposes the local isometric structure into a reciprocal pair, which is metabolic. Its class in is zero and in particular does not have order four.
For , diagonalization givesThe second residue at is the one-dimensional formBecause , and this one-dimensional form is a generator. The P-adic algebraic-concordance obstruction therefore has exact order four, so the image of in has order four.