Bilancini, Ennio; Boncinelli, Leonardo - In: Economics Letters 108 (2010) 1, pp. 13-15
We provide a necessary and sufficient condition for goods to be normal when utility functions are differentiable and strongly quasi-concave. Our condition is equivalent to the condition proposed by Alarie et al. (1990), but it is easier to check: it only requires to compute the minors associated...