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Vanishing algebraic intersection gives geometric disjunction in the simply connected stable range
Statement
Assume . Let be a simply connected oriented smooth manifold and let be closed connected oriented embedded complementary submanifolds with , meeting transversely, with at least one of compact. Suppose the oriented intersection number vanishes: . Then there is an isotopy of carrying to an embedded submanifold transverse to with . More generally, if for some integer , one can isotope so that it meets in exactly points (with the remaining intersections removed in opposite-sign pairs); in particular any two algebraically cancelling pairs can be removed one at a time without creating new intersections. The corresponding statement with group-ring coefficients holds for a general simply connected ambient manifold by the label lemma.
Facts & Assumptions
Compact transverse complementary intersections are finite. Compact transverse complementary intersections are finite
The oriented intersection number. The oriented intersection number
Two points of a closed connected embedded submanifold of dimension at least two can be joined by a smooth embedded arc avoiding a prescribed finite set away from its endpoints. Arcs joining two points of a connected submanifold avoiding finitely many points
In the stable range an admissible opposite-sign pair with nullhomotopic Whitney circle can be removed, leaving every other intersection fixed. The high-dimensional Whitney trick
Proof
Given: Countable choice, simply connected , closed connected oriented complementary transverse sheets of dimensions at least three, and their signed intersection number .
Complementary transversality makes the intersection set discrete. Since one sheet is compact and the other is closed, [F1] makes it finite. If there are positive and negative points, then . Choose disjoint pairs of opposite signs. For each pair the arcs lemma gives sheet arcs avoiding every other intersection, and their circle contracts because is simply connected.
Apply the high-dimensional Whitney trick to one pair at a time. It fixes the other intersection germs, creates no new points, and preserves embeddedness and connectedness of the moved sheet. The next pair therefore has the same signs and can be treated in the same way. After finitely many steps exactly points remain, all of one sign. Reparametrize the finitely many isotopies to be stationary near their endpoints and concatenate them smoothly. In particular gives disjunction. In the simply connected case all group labels are the identity, so its group-ring formulation has exactly this signed-pair computation.
Depends on
- The high-dimensional Whitney trick
- Arcs joining two points of a connected submanifold avoiding finitely many points
- The fundamental-group label controls contractibility of the Whitney circle
- The oriented intersection number
- The local oriented intersection sign
- Intersection number under factor interchange
- Negative expected dimension forces empty generic intersections
- Simply connected topological spaces
- Strong Whitney approximation by transverse maps
- Compact transverse complementary intersections are finite
- The Axiom of Countable Choice ($\mathrm{AC}_\omega$)
Used by
Nothing in the library uses this result yet.
Dependency tree · two levels
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Sources
- Andrew Ranicki, Algebraic and Geometric Surgery (Oxford Mathematical Monographs, Oxford University Press 2002; complete electronic copy) (standard reference, not scraped)
- Wolfgang Lück, A Basic Introduction to Surgery Theory (complete lecture notes, ICTP/Münster) (standard reference, not scraped)