Formalizing a discrete model of the continuum in Coq from a discrete geometry perspective

Abstract

This work presents a formalization of the discrete model of the continuum introduced by Harthong (1989), the Harthong-Reeb line. This model was at the origin of important developments in the Discrete Geometry field (Reveilles and Richard, Ann. Math. Artif. Intell. Math. Inform. 16(14), 89---152 (1996)). The formalization is based on the work presented in Chollet et al. (2012, 2009) where it was shown that the Harthong-Reeb line satisfies the axioms for constructive real numbers introduced by Bridges (1999). Laugwitz-Schmieden numbers (Laugwitz 1983) are then introduced and their limitations with respect to being a model of the Harthong-Reeb line is investigated (Chollet et al., Theor. Comput. Sci. 466, 2---19 (2012)). In this paper, we transpose all these definitions and properties into a formal description using the Coq proof assistant. We also show that Laugwitz-Schmieden numbers can be used to actually compute continuous functions. We hope that this work could improve techniques for both implementing numeric computations and reasoning about them in geometric systems.