Our paper on Assortment Optimization in Sequential Multinomial Logit is online. The framework captures the situation where products are partitioned into two levels, to capture differences in attractiveness, brand awareness and, or visibility in the market. When a consumer is presented with an assortment of products, she first considers products in the first level and, if none of them is purchased, products in the second level are considered. This model is a special case of the Perception-Adjusted Luce Model (PALM) recently proposed recently by Echenique et al. The problem for three or more levels is open … for those interested in a challenge.