7 papers · 1 filter
Immersed projective planes, Arf invariants and even 4-manifolds
Christian Bohr
In this paper, we exploit a subtle indeterminacy in the definition of the spherical Kervaire-Milnor invariant which was discovered by R. Stong to construct non-spin 4-manifolds wit…
Embedded spheres and 4-manifolds with spin coverings
Christian Bohr
A strategy for constructing an embedded sphere in a 4-manifold realizing a given homology class which has been successfully applied in the past is to represent the class as a first…
On the kinkiness of closed braids
Christian Bohr
In this note, we prove a lower bound for the positive kinkiness of a closed braid which we then use to derive an estimate for the positive kinkiness of a link in terms of its Seife…
Homology cobordism and classical knot invariants
Christian Bohr, Ronnie Lee
In this paper we define and investigate Z/2-homology cobordism invariants of Z/2-homology 3-spheres which turn out to be related to classical invariants of knots. As an application…
Cycles, submanifolds, and structures on normal bundles
C. Bohr, B. Hanke, D. Kotschick
We give explicit examples of degree 3 cohomology classes not Poincare dual to submanifolds, and discuss the realisability of homology classes by submanifolds with Spin-C normal bun…
Immersions of surfaces in almost complex 4-manifolds
Christian Bohr
In this note, we investigate the relation between double points and complex points of immersed surfaces in almost-complex 4-manifolds and show how estimates for the minimal genus o…