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Given integers and a constant , consider the space of -tuples of real polynomials in variables of degree , whose coefficients are in absolute value, and satisfying . We study the family of algebraic functions, where is a polynomial, and being a constant depending only on . The main result is a quantitative extension theorem for these functions which is uniform in . This is used to prove Bernstein-type inequalities which are again uniform with respect to .The proof is based on...
When is a polynomial ring or more generally a standard graded algebra over a field , with homogeneous maximal ideal , it is known that for an ideal of , the regularity of powers of becomes eventually a linear function, i.e., for and some integers , . This motivates writing for every . The sequence , called the defect sequence of the ideal , is the subject of much research and its nature is still widely unexplored. We know that is eventually constant. In this article, after...
Let k[[x,y]] be the formal power series ring in two variables over a field k of characteristic zero and let d be a nonzero derivation of k[[x,y]]. We prove that if Ker(d) ≠ k then Ker(d) = Ker(δ), where δ is a jacobian derivation of k[[x,y]]. Moreover, Ker(d) is of the form k[[h]] for some h ∈ k[[x,y]].
The paper establishes the basic algebraic theory for the Gevrey rings. We prove the Hensel lemma, the Artin approximation theorem and the Weierstrass-Hironaka division theorem for them. We introduce a family of norms and we look at them as a family of analytic functions defined on some semialgebraic sets. This allows us to study the analytic and algebraic properties of this rings.
We show that the S-Euclidean minimum of an ideal class is a rational number, generalizing a result of Cerri. In the proof, we actually obtain a slight refinement of this and give some corollaries which explain the relationship of our results with Lenstra's notion of a norm-Euclidean ideal class and the conjecture of Barnes and Swinnerton-Dyer on quadratic forms. In particular, we resolve a conjecture of Lenstra except when the S-units have rank one. The proof is self-contained but uses ideas from...
L. Makar-Limanov, P. van Rossum, V. Shpilrain and J.-T. Yu solved the stable equivalence problem for the polynomial ring k[x,y] when k is a field of characteristic 0. In this note we give an affirmative solution for an arbitrary field k.
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