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On glueing curves on surfaces and zero cycles

Hursit Önsiper (1994)

Atti della Accademia Nazionale dei Lincei. Classe di Scienze Fisiche, Matematiche e Naturali. Rendiconti Lincei. Matematica e Applicazioni

The structure of the group H 2 X , K 2 of a surface X with prescribed singularities is investigated.

On gradient at infinity of semialgebraic functions

Didier D'Acunto, Vincent Grandjean (2005)

Annales Polonici Mathematici

Let f: ℝⁿ → ℝ be a C² semialgebraic function and let c be an asymptotic critical value of f. We prove that there exists a smallest rational number ϱ c 1 such that |x|·|∇f| and | f ( x ) - c | ϱ c are separated at infinity. If c is a regular value and ϱ c < 1 , then f is a locally trivial fibration over c, and the trivialisation is realised by the flow of the gradient field of f.

On gradients of functions definable in o-minimal structures

Krzysztof Kurdyka (1998)

Annales de l'institut Fourier

We prove the o-minimal generalization of the Łojasiewicz inequality grad f | f | α , with α &lt; 1 , in a neighborhood of a , where f is real analytic at a and f ( a ) = 0 . We deduce, as in the analytic case, that trajectories of the gradient of a function definable in an o-minimal structure are of uniformly bounded length. We obtain also that the gradient flow gives a retraction onto levels of such functions.

On higher dimensional Hirzebruch-Jung singularities.

Patrick Popescu-Pampu (2005)

Revista Matemática Complutense

A germ of normal complex analytical surface is called a Hirzebruch-Jung singularity if it is analytically isomorphic to the germ at the 0-dimensional orbit of an affine toric surface. Two such germs are known to be isomorphic if and only if the toric surfaces corresponding to them are equivariantly isomorphic. We extend this result to higher-dimensional Hirzebruch-Jung singularities, which we define to be the germs analytically isomorphic to the germ at the 0-dimensional orbit of an affine toric...

On homotopy types of limits of semi-algebraic sets and additive complexity of polynomials

Sal Barone, Saugata Basu (2014)

Journal of the European Mathematical Society

We prove that the number of distinct homotopy types of limits of one-parameter semi-algebraic families of closed and bounded semi-algebraic sets is bounded singly exponentially in the additive complexity of any quantifier-free first order formula defining the family. As an important consequence, we derive that the number of distinct homotopy types of semi-algebraic subsets of k defined by a quantifier-free first order formula Φ , where the sum of the additive complexities of the polynomials appearing...

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