Alphabeta Math
LemmaStatement: AI-adaptedProof: AI-generated
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 i:S1→R2, i(x1,x2)=(x1,x2), and r:S1→R2, r(x1,x2)=(x1,−x2), 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 S1=∂D2 with boundary orientation, and i,r as stated.

[F1]

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).

[F2]

A coordinate reflection of the circle has degree −1; an orientation-preserving circle diffeomorphism has degree 1, 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).

[F3]

For a self-transverse immersion Mm→X2m 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

1.1givenF3constructalgebra

Both maps are embeddings. The radial fields ni(x)=x and nr(x)=r(x) are smooth nowhere-zero normal vectors: reflection preserves the inner product, so ⟨r(x),drx(v)⟩=⟨x,v⟩=0 for tangent vectors v. They trivialize the normal lines. Both double point sets are empty, so self-transversality is vacuous and [F3] gives zero primary counts.

1.2F1givenconstruct

Suppose an isotopy exists. By [F1] its ambient extension has time-one diffeomorphism H with H∘i=r. Its orientation sign is positive, since the differential determinants of the ambient isotopy vary continuously from the identity and never vanish. Also H(S1)=S1. The plane complement consists of the open disk and its exterior, and H 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 H(D2)=D2.

2.1F2step 1.1step 1.2∎

The orientation-preserving disk diffeomorphism H∣D2 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 H∣S1 has degree 1 by [F2]. But H∘i=r identifies this restriction with the coordinate reflection of degree −1, a contradiction. Thus the embeddings are not isotopic, while their normals and primary counts agree by step 1.1.

Depends on

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