We adopt Vergnaud’s (2009) theory of conceptual fields where a concept is a triplet of a set: C=(S, I, L) where S stands for the set of situations which give sense to a concept (the referent); I stands for the set of operational invariants associated to the concept (the meaning); L stands for the set of linguistic and non-linguistic representations which allow for the symbolic representation of a concept, its attributes, the situation to which it applies and the procedures it nourishes