Limit Filters and Dependent Choice in Countable-Support Symmetric Iterations
Abstract
We isolate an algebraic limit-filter construction for countable-support symmetric iterations built from coherent successor-stage symmetric systems. At limits of uncountable cofinality, countably many generators and their conjugating automorphisms are bounded below the limit; at limits of cofinality $ω$, countable-intersection closure is imposed in the definition. The resulting limit filters are normal and $ω_1$-complete. This gives a ground-coded syntactic closure result: the canonical tuple of a ground-model countable sequence of hereditarily symmetric names is hereditarily symmetric. We also recall the standard symmetric-extension theorem yielding $\mathrm{ZF}$ from a genuine symmetric system. The previously claimed preservation of $\mathrm{DC}$ and the unordered-pairs application are withdrawn. Filter completeness alone does not turn the ground-coded tuple statement into closure under arbitrary countable sequences in the forcing extension. Moreover, every nonempty finite set of reals has a lexicographically least element in $\mathrm{ZF}$, so a family of two-element sets of reals without a choice function cannot exist. The present paper retains only the corrected limit-filter observations and the explicitly qualified symmetric-name consequences.
Fields of Study & Subjects
Advanced Topology and Set Theory
Mathematical and Theoretical Analysis
Advanced Banach Space Theory
Publication details
- Journal / source
- arXiv (Cornell University)
- Publication date
- 16 January 2026
- Document type
- Preprint