Alphabeta Math
CounterexampleConstruction: Literature-sourcedVerification: AI-generatedprecheck passaudited 2026-08-31
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  • 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.
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The punctured disc is connected but not simply connected

Statement refuted

Every connected subdomain of the unit disc is simply connected.

Facts & Assumptions

Given: The punctured disc Ω={zC:0<z<1} and the circle γ(t)=12eit on [0,2π].

[L1]
[L2]

A circle around the origin has winding number 1 about the origin (A circle traversed k times has winding number k inside and 0 outside).

Counterexample

technique · direct
1.1

The punctured disc is open and connected, and the loop γ lies in it. Its spherical complement is the union of the singleton {0} and the outer region {z1}{}, so it is disconnected.

given
2.1

By [L1], step 1.1 shows that the punctured disc is not simply connected. Fact [L2] gives the same geometric reason numerically: the loop γ still winds once around the omitted point 0.

step 1.1L1L2
3.1

This refutes the claim.

step 1.1step 2.1

Depends on

Used by

Nothing in the library uses this result yet.

Dependency tree · two levels

42 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