2020/01/01 by Boris Tsirelson · 1 citation
Computer Science · Mathematics · #Computability, Logic, AI Algorithms #History and Theory of Mathematics #Advanced Topology and Set Theory
paper · doi:10.15347/wjs/2020.008
openalex publication_date 2020/01/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Contrary to popular misconception, the question in the title is far from simple. It involves sets of numbers on the first level, sets of sets of numbers on the second level, and so on, endlessly. The infinite hierarchy of the levels involved distinguishes the concept of "definable number" from such notions as "natural number", "rational number", "algebraic number", "computable number" etc.