Positive Legendrian regular homotopies

Embeddings of Surfaces into 3-Space and Quadruple Points of Regular Homotopies

Let F be a closed orientable surface. We give an explicit formula for the number mod 2 of quadruple points occurring in any generic regular homotopy between any two regularly homotopic embeddings e,e':F -> R^3. The formula is in terms of homological data extracted from the two embeddings.

Subgroups of the Mapping Class Group and Quadruple Points of Regular Homotopies

Let F be a closed orientable surface. If i,i':F \to R^3 are two regularly homotopic generic immersions, then it has been shown in [N] that all generic regular homotopies between i and i' have the same number mod 2 of quadruple points. We denote this number by Q(i,i') \in Z/2. We show that for any generic immersion i:F\to R^3 and any diffeomorphism h:F\to F such that i and i\circ h are regularly homotopic, Q(i,i\circ h) = (rank(h_*-Id) + (n+1)e(h)) mod 2, where h_* is the map induced by h on H_1(F,Z/2), n is the genus of F and e(h) is 0 or 1 according to whether h is orientation preserving or r…

Quadruple Points of Regular Homotopies of Surfaces in 3-Manifolds

Let GI denote the space of all generic immersions of a surface F into a 3-manifold M. Let q(H_t) denote the number mod 2 of quadruple points of a generic regular homotopy H_t : F -> M. We are interested in defining an invariant Q : GI -> Z/2 such that q(H_t) = Q(H_0) - Q(H_1) for any generic regular homotopy H_t : F -> M. Such an invariant exists iff q=0 for any "closed" generic regular homotopy (abbreviated CGRH.) Max and Banchoff proved that for any CGRH H_t: S^2 -> R^3 indeed q(H_t)=0. We generalize their result as follows: Theorem 3.9: Let F be a system of closed surfaces, and let H_t : F …

There are non homotopic framed homotopies of long knots

Let $\mathcal {M}$ be the space of all, including singular, long knots in 3-space and for which a fixed projection into the plane is an immersion. Let $cl(Σ^{(1)}_{iness})$ be the closure of the union of all singular knots in $\mathcal {M}$ with exactly one ordinary double point and such that the two resolutions represent the same (non singular) knot type. We call $Σ^{(1)}_{iness}$ the {\em inessential walls} and we call $\mathcal {M}_{ess} = \mathcal {M} \setminus cl(Σ^{(1)}_{iness})$ the {\em essential diagram space}. We construct a non trivial class in $H^1(\mathcal {M}_{ess}; \mathbb{Z}[A,…

关于紧致正则 $(κ, μ)$-流形的若干刚性结果

On Certain Rigidity Results of Compact Regular $(κ, μ) $-Manifolds

本文研究闭正则非 Sasakian $(κ, μ)$-流形 Boothby-Wang 纤维化底空间的度量刚性，利用保持双 Legendrian 结构的投影偏差，统一证明 Riemann 情形的 Sasakian 结构唯一性及半 Riemann 情形的有限仿切触结构分类。

Functoriality of the EH class and the LOSS invariant under Lagrangian concordances

We show that the EH class and the LOSS invariant of Legendrian knots in contact 3-manifolds are functorial under regular Lagrangian concordances in Weinstein cobordisms. This gives computable obstructions to the existence of regular Lagrangian concordances.