Judge Guido Calabresi’s new book (2016) ‘The Future of Law and Economics – Essays in Reform and Recollection’ not only represents a master piece but also, paraphrasing a sentence by the Author himself, a ‘pearl beyond price’ , a new door opened to a deeper insight on the existing relationship between Legal Theory and Economics or, more generally speaking, between ‘Law and ...’. 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 I will borrow some of the elements of the theory of sets (particularly the concept and some of the operations on sets) and I’ll start with Judge Calabresi’s distinction, often disregarded by the literature, between Economic Analysis of Law and Law and Economics, 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 book Tragic Choices. Even if the usage of the theory of sets I make is intuitive, in the appendix I review so-me of its basics.