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.
Under choice, every metrizable space has
Statement
Assuming choice, every metrizable space satisfies under the raw convention.
Facts & Assumptions
Given: The Axiom of Choice, a metric inducing the topology of , and a dense set of least cardinality .
The rationals are countably infinite and lie densely between reals ( is countably infinite, The rationals embed densely in the reals).
Proof
Suppose first that is infinite. The family has cardinality at most by [L2] and [L3]. It is a basis: if with open, choose with , choose with , and then by [L2] choose a positive rational with . Thus . Hence .
Suppose is finite. If , density forces and both raw invariants are . Otherwise : if , the finitely many positive distances for have a positive minimum, and a smaller ball about misses , contradicting density. A finite metric space is discrete, since at each point a ball smaller than all distances to the other finitely many points is a singleton. The singleton family is a basis of size , and every basis of a discrete space must contain each singleton; also every dense set must contain every point. Therefore .
Step 1.1 handles infinite density and step 1.2 handles finite density; combining the resulting upper bound with [L1] gives in every case.
Depends on
- Under choice, $c(X)\le d(X)\le w(X)$ and $\chi(X),L(X)\le w(X)$
- Metrizable space: a topological space whose topology is induced by some metric; metrizability is topological, the metric is not
- The metric topology: a set is open when every one of its points has a ball around it inside the set; closed means open complement
- $\mathbb{Q}$ is countably infinite
- The rationals embed densely in the reals
- Cardinal sum $\kappa \oplus \lambda$, product $\kappa \otimes \lambda$ and exponentiation $\kappa^{\lambda}$, and why they are written apart from the ordinal operations
- Absorption: for cardinals $\kappa, \lambda$ with $\kappa$ infinite and $\lambda \le \kappa$, $\kappa \oplus \lambda = \kappa$, and $\kappa \otimes \lambda = \kappa$ when $\lambda \ne 0$
- The Axiom of Choice
Used by
Dependency tree · next 3 levels
Direct dependencies and their dependencies through the next three levels: 180 results over 31 levels. An arrow runs from a result to what uses it, and this result sits at the bottom with a heavier outline. Click the chart to enlarge it.
Sources
- D. H. Fremlin, Measure Theory, Chapter 5A (standard reference, not scraped)