ABSTRACT
The chapter describes briefly the relevant bits of the path Sraffa's work took in the first period devoted to what in December 1927 he called 'la mia teoria' and his 'libro' which extended roughly from late 1927 to the end of 1931. While Sraffa in the first period of his work had made a few attempts to acquaint him with the relevant mathematical tools. The chapter turns to the collaboration between the two men, who soon got on friendly terms with one another, on what Sraffa called the 'proof of the gradient', an expression partially adopted from Besicovitch. This section focuses on the path that led to the proof of the gradient with regard to single-products systems. Sraffa also attempted to generalize the proof to systems with joint production. It deals with few further notes drafted by Sraffa in 1945 in which he pointed out some of the properties of the systems of production that followed from the gradient argument.
