Compact, $C^2$-foliated manifolds of codimension one, having all leaves proper, are shown to be $C^{\infty }$-smoothable. More precisely, such a foliated manifold is homeomorphic to one of class $C^{\infty }$. The corresponding statement is false for foliations with nonproper leaves. In that case, there are topological distinctions between smoothness of class $C^r$ and of class $C^{r+1}$ for every nonnegative integer $r$.

Define for a smooth compact hypersurface $M^n$ of ${\mathbf{R}}^{n+1}$ its crumpleness $\kappa \left(M^n\right)$ as the ratio ${diam}_{{\mathbf{R}}^{n+1}}(M^n)/r(M^n)$, where $r\left(M^n\right)$ is the distance from $M^n$ to its central set. (In other words, $r\left(M^n\right)$ is the maximal radius of an open non-selfintersecting tube around $M^n$ in ${\mathbf{R}}^{n+1}.)$We prove that any $n$-dimensional non-singular compact algebraic hypersurface of degree $d$ is rigidly isotopic to an algebraic hypersurface of degree $d$ and of crumpleness $\le exp\left(c\right(n\left)d^{\alpha \left(n\right)d^{n+1}}\right)$. Here $c\left(n\right)$, $\alpha \left(n\right)$ depend only on $n$, and rigid isotopy means an isotopy passing only through hypersurfaces of degree...

Families of codimension-one foliations and laminations are constructed in certain 3-manifolds, with the property that their transverse intersection with the boundary torus of the manifold consists of parallel curves whose slope varies continuously with certain parameters in the construction. The 3-manifolds are 2-bridge knot complements and punctured-torus bundles.

One wonders or not whether it is possible to determine the homotopy class of a vector field by examining some algebraic invariants associated with its qualitative behavior. In this paper, we investigate the algebraic invariants which are usually associated with the periodic solutions of non-singular Morse-Smale vector fields on the 3-sphere. We exhibit some examples for which there appears to be no correlation between the algebraic invariants of the periodic solutions and the homotopy classes of...

Let $S^3$ denote the set of points with modulus one in euclidean 4-space $R^4$ ; and let ${\Gamma }_0^1(S^3)$ denote the space of nonsingular vector fields on $S^3$ with the $C^1$ topology. Under what conditions are two elements from ${\Gamma }_0^1(S^3)$ homotopic ? There are several examples of nonsingular vector fields on $S^3$. However, they are all homotopic to the tangent fields of the fibrations of $S^3$ due to H. Hopf (there are two such classes).We construct some new examples of vector fields which can be classified geometrically. Each of these examples...