This pinned Lean source formalizes the following mathematical result: In the checked nondegenerate butterfly configuration, the opposite-chord intersections X and Y have the original chord midpoint M as their midpoint. Download the complete checked closure or open its single Lean endpoint to study the proof or develop an extension.
Each ZIP contains the checked first-party local Lean import closure, exact statements and boundaries, license, notice, evidence, a source-footprint manifest, and an agent continuation file. Mathlib and other third-party dependencies are not bundled; this is not a portable whole-repository release.
How counting works: Line counts exclude blank lines; comments and documentation count. The total is the deduplicated, commit-pinned first-party Lean import closure; Mathlib and other third-party dependencies are excluded. Declaration count means names covered by the artifact's recorded evidence; it is not a count of every declaration in the source. Source footprint is not a difficulty or proof-quality score.
This closure supports the theorem evidence record above.
This theorem's complete first-party Lean closure is the single main file shown above: 3,197 lines. External Mathlib modules remain dependency-locked separately.
Source hashMatches checked record
Lean buildPassed in recorded evidence
LicenseApache-2.0 · Advameg, Inc.
Provenance and reproducibility
Exact checked source, with reuse terms
The endpoint and every listed local import come from the exact recorded Git commit, and the endpoint matches the stored source hash byte for byte. The locally authored package material is licensed under Apache-2.0 by Advameg, Inc.; Mathlib and cited third-party material remain under their own terms. Machine-readable checker evidence is included.