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 teaching sequences based on the use of such DGS and analyse the possible roles of DGS in both the teaching and learning of proof. This paper is a reaction to these four papers. Starting from them, it attempts to develop a global discussion about the roles of DGS, by addressing four points: the variety of possible contexts for proof in a DGS, the dual nature of proof (cognitive and social) as reflected in the 'milieu' constructed around the use of a DGS, from observing to proving, and the overcoming of the opposition between doing and proving. © 2001 Kluwer Academic Publishers.