This paper reinterprets, differently from the existing literature, the relationship between law and economics not from the point of view of a lawyer-economist but rather from the point of view of an economist-mathematician, and it raises a methodological issue. To do so, some of the elements of the theory of sets are borrowed to argue that behavioral economics, its application to behavioral law and economics, and behavioral economists have generalized the pioneering work of Judge Calabresi, with reference to the famous books ‘Tragic Choices’ and ‘The Future of Law and Economics – Essays in Reform and Recollection’. Even if the usage of the theory of sets made in this paper is intuitive, some of its basics are reviewed in the appendix.