We present a novel logic-based approach to automate multi-issue bilateral negotiation in e-marketplaces. In such frameworks issues to negotiate on can be multiple, interrelated, and may not be fixed in advance. We use logic to model relations among issues and to allow agents express their preferences on them. In particular, we introduce the logic , a fuzzy propositional logic extended with concrete domains in order to handle numerical, as well as non numerical features, and to deal with vagueness in buyer/seller preferences. Hence, agents can express preferences as e.g., I am searching for a passenger car costing about 25000€ yet if the car has a GPS system and more than two-year warranty I can spend up to 28000€.