Herewith a few comments on the books I recommended dealing with the modern mathematical reinterpretation of Marx's economic theories. The comments make it clear that there are many other more recent works that I have failed to keep up with. All additions and comments gratefully accepted.
1. Piero Sraffa, PRODUCTION OF COMMODITIES BY MEANS OF COMMODITIES This is an extraordinary work, totally different from CAPITAL in tone and style, but fully as compelling and distinctive. Sraffa writes as though he were a monk who, after forty years of meditation on the scriptures, now begins softly, without haste, to speak. The first sentence of the little book is: "Let us consider an extremely simple society which produces just enough to maintain itself." As I remarked, the math is dead simple, but Sraffa, like many theorists, omits intermediate steps quite often, with the result that it sometimes took me hours to read a page, reconstructing the steps and refusing to move on until I understood exactly how each step followed from the one before. Reading the book was an intellectual [and dare I say it, spiritual] experience for me quite like any other.
2. Michio Morishima, MARX'S ECONOMICS I found this a difficult book to work through, and you might want to move on to some of the others, but it played an important role in the development of the movement.
3. Luigi Pasinetti, GROWTH AND INCOME DISTRIBUTION and LECTURES ON THE THEORY OF PRODUCTION. I found Pasinetti very helpful. His writing is quite accessible, albeit rigorous. He is especially good at making the connections between Marx and his predecessors -- most notably Ricardo and the Physiocrats. He even includes an appendix in which he presents the elements of linear algebra.
4. Andras Brody, PROPORTIONS, PRICES, AND PLANNING. I found this a fascinating book for two reasons: First of all, Brody was writing in Hungary, during a time when the government was engaging in economic planning, so, unlike all of the other authors, he is actually concerned with the application of the theory to practice; and Second, in total contrast to all the other authors, Brody worries about whether the units in an equation are compatible. This may seem like a rather minor matter, but I found it quite helpful and refreshing.
5. Abraham-Frois and Berrebi, THEORY OF VALUE, PRICES AND ACCUMULATION. A difficult but important book, that includes a very helpful discussion of joint production, a problem in linear production models on which a lot of ink has been spilled. One of the curious and interesting things in the book is an extremely arcane analysis of a special case in which one of Marx's central propositions holds true. Roughly speaking, the story is this: In explaining why prices deviate from labor values in the general case in which there is not equal organic composition of capital in all industries [the case analyzed in Volume One of CAPITAL], Marx argues that the identity of profit and surplus value is maintained in the economy as a whole. It turns out that this is not true generally, but is true, remarkably enough, just in case the economy is embarked on a von Neumann balanced growth path. [This involves there being no luxury consumption, all profits being plowed back into capital expansion -- "Accumulate, accumulate, that is Moses and the Prophets to the capitalists" as Marx says in one wonderful passage.] It had been thought that this was the necessary as well as the sufficient condition for Marx's claim to be true, but Abraham-Frois and Berrebi show that there is a very obscure situation, having to do with the maximal eigenvalues of the unit input matrix, in which Marx's claim also holds. For the specialist!
6. Ian Steedman, MARX AFTER SRAFFA. This is one of the most extraordinary books I have ever read. It is, if I may put it this way, a furiously angry work of mathematics! Steedman is [was?] a British communist who was fed up with his traditionalist colleagues in the Party who insisted on holding to the old bedtime stories about surplus value and all, even after Sraffa had shown that one needed a new, cleaned up version of the critique of capitalism. He plays out all manner of supposed ridiculous conclusions one can draw from the old Marxist story, such as the fact that with joint production, some labor values turn out to be negative. He surely must have been a young man when he wrote this book, and he just cannot contain his scorn for those who hew to the old ways without knowing any math. It is a great read, and lots of fun. By the way, I think he is essentially wrong, but that is a long, long story.
7. John Roemer, ANALYTICAL FOUNDATIONS OF MARXIAN ECONOMIC THEORY. This is a simply terrific book, difficult in its math parts, but absolutely clear in its exposition. One of Roemer's many important insights [which he urged against me in a comment on a paper I wrote and published] is that exploitation is possible even in the absence of a labor market, by way of structures of debt that effectively enslave and exploit workers or peasants. If you are going to read only one book on this list, and are willing to do the work, this might be the best choice.
8. Walsh and Gram, CLASICAL AND NEOCLASSICAL THEORIES OF GENERAL EQUILIBIUM I don't really recommend that you read this, but I include it for two reasons. First of all, when I started reading all this literature, I became very excited about it. At the time, I was very close to Sam Bowles, Herb Gintis, and the other radicals in the UMass econ department. It seemed to me that the success of this alternative approach to economics would require a way of teaching it at the intro level as perspicuous and elegant as that created by Samuelson and others with their familiar little supply and demand curves. I knew I could not do it, but I hoped against hope that Sam would try, since he was [and is] the smartest of the radicals. But he and Herb got interested in Game Theory [which I thought was a mistake] and went in another direction. Anyway, Walsh and Gram attempt a geometric representation of the linear programming models underlying the classical and Marxian approach, so I read their book with great anticipation [but eventual disappointment]. The other reason is a funny story. I had met John Kenneth Galbraith in the senior common room of Winthrop House at Harvard, although of course he did not remember that. Anyway, I was on a plane returning from a talk in Ohio, and in those days the American Airlines jets were configured so that in the first two rows, six people sat, three and three, facing one another across a table. I sat down in one of the seats, and catty-corner across from me was none other than Galbraith, crammed into the seat [he was 6'7"]. I had the Walsh and Gram with me on the table, reading it, and at one point Galbraith reached a long arm across the table and took the book to look at it, without so much as a word. I told him what it was about, and he looked at it and handed it back. He was at that point traveling and campaigning for Teddy Kennedy, who was making an unsuccessful run for the Democratic presidential nomination. It was the next to the last time I met Galbraith.