722 research outputs found
Unoriented geometric functors
Farrell and Hsiang noticed that the geometric surgery groups defined By Wall,
Chapter 9, do not have the naturality Wall claims for them. They were able to
fix the problem by augmenting Wall's definitions to keep track of a line
bundle.
The definition of geometric Wall groups involves homology with local
coefficients and these also lack Wall's claimed naturality.
One would hope that a geometric bordism theory involving non-orientable
manifolds would enjoy the same naturality as that enjoyed by homology with
local coefficients. A setting for this naturality entirely in terms of local
coefficients is presented in this paper.
Applying this theory to the example of non-orientable Wall groups restores
much of the elegance of Wall's original approach. Furthermore, a geometric
determination of the map induced by conjugation by a group element is given.Comment: 12 pages, LaTe
Codimension one spheres which are null homotopic
This paper classifies embedded, codimension-one spheres which are null
homotopic. This information is used to show that all null homotopic, immersed
codimension-one spheres which are taut in the sense of Terng and Thorbergsson
are actually distance spheres.Comment: 6 page
An invariant of smooth 4-manifolds
We define a diffeomorphism invariant of smooth 4-manifolds which we can
estimate for many smoothings of R^4 and other smooth 4-manifolds. Using this
invariant we can show that uncountably many smoothings of R^4 support no Stein
structure. (Gompf has constructed uncountably many smoothings of R^4 which do
support Stein structures.) Other applications of this invariant are given.Comment: 19 pages. Published copy, also available at
http://www.maths.warwick.ac.uk/gt/GTVol1/paper6.abs.htm
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