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Formalizing Pick's Theorem in Isabelle/HOL
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Formalizing Pick's Theorem in Isabelle/HOL

Sage Binder and Katherine Kosaian
ArXiv.org
Cornell University
05/03/2024
DOI: 10.48550/arxiv.2405.01793
url
https://doi.org/10.48550/arxiv.2405.01793View
Preprint (Author's original)This preprint has not been evaluated by subject experts through peer review. Preprints may undergo extensive changes and/or become peer-reviewed journal articles. Open Access

Abstract

We formalize Pick's theorem for finding the area of a simple polygon whose vertices are integral lattice points. We are inspired by John Harrison's formalization of Pick's theorem in HOL Light, but tailor our proof approach to avoid a primary challenge point in his formalization, which is proving that any polygon with more than three vertices can be split (in its interior) by a line between some two vertices. We detail the approach we use to avoid this step and reflect on the pros and cons of our eventual formalization strategy. We use the theorem prover Isabelle/HOL, and our formalization involves augmenting the existing geometry libraries in various foundational ways (e.g., by adding the definition of a polygon and formalizing some key properties thereof).
Computer Science - Logic in Computer Science

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