Is it possible to study the ergonomic affordances offered by a system designed for educational aims and their transformation into cultural affordances? To this purpose, what references can we adopt? This work describes the theoretical framework used to realise this study referring to AlNuSet, a system realised within the EC ReMath project to support the teaching and learning of algebra. The framework is centred on the notions of ergonomic and cultural affordance introduced Turner & Turner and the cycle of expansive learning elaborated by Engestrom. (Contains 2 figures and 1 table.)