How statement and proof provenance work
The first chip identifies the source of the statement or construction; the second identifies the source of its local proof or verification.
- Literature-sourced: the exact statement appears in a cited source; only wording and notation differ.
- AI-adapted: a semantically identical restatement of literature-sourced material, modulo indexing, notation, and boundary cases adopted by the library.
- AI-generated: a genuinely novel statement formulated by AI, with no source for the claim itself.
These labels describe origin, not correctness: citations and verification chips remain separate evidence.
The basic Cohen set has no countably infinite subset
Statement
Every map from into in the basic Cohen model has finite range; therefore no injection , no countably infinite subset, and no enumeration of exists.
Facts & Assumptions
Given: The hypotheses, objects, and conventions in the Statement.
The Cohen reals form a symmetric set but their enumeration is not symmetric states the exact coordinate action , pairwise distinctness, and infinitude of .
Symmetry lemma for forcing automorphisms transports decisions under swaps.
Proof
Let , and enlarge a finite support of to support . If some forces with , choose outside and outside the first-coordinate support of . Let swap . Then , , and F2 gives .
The conditions and agree wherever both are defined: the coordinate was fresh and all other moved coordinates are fixed. Their union is a common extension forcing , contradicting F1. Hence no extension of can put a value outside , and density of decisions yields .
Thus every such map has finite range, so none is injective or enumerates the infinite set . A countably infinite subset would, by its meaning in ZF, carry a bijection from and hence an injection into , also impossible. Fresh indices were chosen only from explicit complements of finite sets; no AC is used.
Depends on
Used by
Dependency tree · two levels
7 results within two dependency steps of this one, each drawn at its shortest distance from it. An arrow runs from a result to what uses it, so the chart reads left to right and ends at this result, which carries a heavier outline. Every node is a link to that result. Click elsewhere on the chart to enlarge it.
Sources
- Karagila, Forcing & Symmetric Extensions, Theorem 10.25 (standard reference, not scraped)