[Paper Review] Crónica de un contraejemplo

Daniel Duarte|arXiv (Cornell University)|Jan 10, 2026

Psychological Treatments and Disorders0 citations

TL;DR

The paper narrates the five-decade history of Nash blowups in resolving singularities, culminating in a 2024 counterexample showing Nash blowups do not, in general, resolve singularities.

ABSTRACT

In the 1960s, John Nash proposed a method to resolve singularities. Five decades of encouraging results could not prevent an unexpected ending: the method does not work in general. In this note (written in Spanish), we tell the story of the rise and fall of the Nash blowup.

Motivation & Objective

• Motivate the study of singularities and the Nash blowing-up approach as proposed by Nash.
• Provide a chronological survey of major results from 1975 to 2025 on Nash blowups.
• Highlight the emergence of a counterexample in 2024 and its implications for resolution in various characteristics.

Proposed method

• Introduce the Nash blowup construction via the Gauss map and tangent spaces.
• Survey key results by dimension and setting, focusing on characteristic zero, positive characteristic, and toric varieties.
• Explain the normalized Nash blowup and its relation to ideal-theoretic and combinatorial data.
• Describe computational approaches and explicit examples leading to counterexamples in higher dimensions.
• Discuss the positive results for toric and determinantally generic varieties and their characteristic dependence.

Experimental results

Research questions

• RQ1 Does the Nash blowup (and its normalized form) resolve singularities in general?
• RQ2 Is the behavior of Nash blowups independent of the field characteristic for broad classes of varieties?
• RQ3 Can the Nash blowup approach be made canonical or algorithmic for resolution across dimensions and characteristics?
• RQ4 What specific classes of varieties (e.g., toric, determinantal) exhibit characteristic-free resolution by Nash blowups?

Key findings

• A long-established program of Nash blowups does not universally resolve singularities, as shown by a counterexample in 2024.
• For toric varieties and certain two-dimensional cases, Nash blowups yield results consistent with resolution, including characteristic-free behavior under specific hypotheses.
• Positive results extend to toric surfaces and some determinantal varieties, including dimension two and parts of dimension three under varying conditions.
• In dimension four and higher, explicit counterexamples demonstrate that Nash blowups can fail to resolve singularities even after iteration.
• Computational work and new constructions (including Reeves cone-based examples) reveal the intricate dependence on dimension and characteristic.
• The narrative shows the revival of interest in Nash blowups, with ongoing research in multiple dimensions and characteristics.