[cliquer ici pour la version en français] Amos Tversky works have shown that human similarity judgement is not a metric (in a mathematic sens). In particular the following properties are not always verified: Minimality : \delta(a,b) \geq \delta(a, a) = 0. Symmetry : \delta(a, b) = \delta(b, a). Triangular inequality : \delta(a, b) + \delta(b, [...]