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 round circle and its reflection are not isotopic embeddings in the plane
Statement
Assume AC. The embeddings , , and , , have trivial normal lines and empty double point sets, but are not isotopic as parametrized embeddings. Their primary unoriented double point counts are both zero.
Facts & Assumptions
Given: AC, the unit circle with boundary orientation, and as stated.
A smooth isotopy of embeddings of a compact source extends to an ambient isotopy, after flattening the time parameter near its ends; the theorem assumes countable choice, supplied by AC (The isotopy extension theorem, AC implies DC implies countable choice, The Axiom of Choice).
A coordinate reflection of the circle has degree ; an orientation-preserving circle diffeomorphism has degree , with the boundary orientation using the outward normal first (Degree of identity constant reflection and antipodal sphere maps, Degree of an orientation-preserving or reversing diffeomorphism, Induced boundary orientation).
For a self-transverse immersion the unoriented primary count is the number of unordered double point pairs modulo two; an embedding has empty pair set (The primary double point obstruction to removing self-intersections).
Proof
Both maps are embeddings. The radial fields and are smooth nowhere-zero normal vectors: reflection preserves the inner product, so for tangent vectors . They trivialize the normal lines. Both double point sets are empty, so self-transversality is vacuous and [F3] gives zero primary counts.
Suppose an isotopy exists. By [F1] its ambient extension has time-one diffeomorphism with . Its orientation sign is positive, since the differential determinants of the ambient isotopy vary continuously from the identity and never vanish. Also . The plane complement consists of the open disk and its exterior, and permutes these components. The image of the closed disk is compact; thus the open disk cannot map to the exterior, whose closure is unbounded. Therefore .
The orientation-preserving disk diffeomorphism carries outward-pointing boundary vectors to outward-pointing vectors: in local boundary coordinates a diffeomorphism preserving the interior has positive inward-coordinate derivative on the boundary. Consequently it preserves the induced boundary orientation, so has degree by [F2]. But identifies this restriction with the coordinate reflection of degree , a contradiction. Thus the embeddings are not isotopic, while their normals and primary counts agree by step 1.1.
Depends on
- The isotopy extension theorem
- Degree of identity constant reflection and antipodal sphere maps
- Degree of an orientation-preserving or reversing diffeomorphism
- Induced boundary orientation
- The primary double point obstruction to removing self-intersections
- AC implies DC implies countable choice
- The Axiom of Choice
Used by
Dependency tree · two levels
47 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
- Morris W. Hirsch, Differential Topology, Chapter 8 section 1, isotopy extension (standard reference, not scraped)