1957. Review of Josef Esser, Grundsatz und Norm in der rechterlichen Fortbildung des Privatrechts: rechtsvergleichende Beiträge zur Rechtsquellen- und Interpretationslehre [Principle and Norm in the Judicial Development of Private Law: A Comparative Inquiry into the Problems of the Sources of Law and Their Interpretation], J.C.B. Mohr/Paul Siebeck (1956) 394 p. in: 24 University of Chicago Law Review (1957) 597-606 [Illustrative excerpt to illustrate relevance to Article 7(2) of the CISG: " A promissor will thus be held to be bound not only to what he has promised expressly but also to numerous 'auxiliary duties' of protecting the interest of the obligee. The latter in turn has been held to be bound to exercise his rights so as not unnecessarily to burden the obligor."]