Eisner v. Maeomber, 252 U.S. 189 (1920), a corporate tax case, was the principal illustration of a theory of legal reasoning and legal argumentation proposed more than ten years ago. Although the theory was described in some detail, using the vocabulary of prototypes and deformations, it was never fully implemented. There were two main problems: (1) the knowledge representation languages available at the time were not sufficiently expressive, and (2) as a result, the central concept of a prototype was never sufficiently formalized. These problems have been remedied by subsequent work, and the present paper describes an implementation (in PlZOLOG) of the original theory. study of the implemented system provides a rational reconstruction of the arguments of Justice Pitney and Justice Brandeis in this seminal corporate tax case.