Formalizing projective plane geometry in Coq

  • Authors:
  • Nicolas Magaud;Julien Narboux;Pascal Schreck

  • Affiliations:
  • LSIIT UMR 7005 CNRS - Université de Strasbourg;LSIIT UMR 7005 CNRS - Université de Strasbourg;LSIIT UMR 7005 CNRS - Université de Strasbourg

  • Venue:
  • ADG'08 Proceedings of the 7th international conference on Automated deduction in geometry
  • Year:
  • 2008

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Abstract

We investigate how projective plane geometry can be formalized in a proof assistant such as Coq. Such a formalization increases the reliability of textbook proofs whose details and particular cases are often overlooked and left to the reader as exercises. Projective plane geometry is described through two different axiom systems which are formally proved equivalent. Usual properties such as decidability of equality of points (and lines) are then proved in a constructive way. The duality principle as well as formal models of projective plane geometry are then studied and implemented in Coq. Finally, we formally prove in Coq that Desargues' property is independent of the axioms of projective plane geometry.