Dynamic Geometry Environments as a Source of Rich Learning Contexts for the Complex Activity of Proving

Is proof activity in danger with the use of dynamic geometry systems(DGS)? The papers of this special issue report about various teachingsequences based on the use of such DGS and analyse the possible roles ofDGS in both the teaching and learning of proof. This paper is a reaction tothese four papers. Starting from them, it attempts to develop a globaldiscussion about the roles of DGS, by addressing four points: the variety ofpossible contexts for proof in a DGS, the dual nature of proof (cognitiveand social) as reflected in the `milieu' constructed around the use of aDGS, from observing to proving, and the overcoming of the oppositionbetween doing and proving.