Effective Bounds on Topological Types of Real Algebraic and Semialgebraic Sets

Abstract

In this paper, we revisit the problem of classifying real algebraic and semialgebraic sets by their topological types, focusing on establishing the effectiveness of bounds rather than deriving new quantitative estimates. Building on Hardt's theorem and leveraging a model-theoretic framework, we prove the existence of effective bounds on the number of distinct topological types for real algebraic sets defined by polynomials of bounded degree. While less precise than previously known doubly exponential bounds derived from methods such as Stratified Cylindrical Algebraic Decomposition, our results are obtained with minimal additional work, emphasizing simplicity and uniformity. Additionally, we establish the existence of an effective bound on the complexity of the semialgebraic homeomorphisms that describe representatives of the topological equivalence classes, offering a novel perspective on their explicit classification. These findings complement existing results by demonstrating the effectiveness of uniform bounds within a logical and geometric framework. The paper concludes with an extension of these results to semialgebraic sets of bounded complexity, further emphasizing the uniformity of the approach across varying real closed fields.