Cohn, Free Rings and Their signs. Academic Press, London-New York, 1985. Reiner, Methods of Representation Theory I, II. John Wiley and Sons, New York, 1990. bursts on Representation Theory. Faith, Algebra: Rings, Modules and Categories. Springer-Verlag, BerlinHeidelberg- New York, 1973.Weibel, An download традиция to abelian integration, Cambr. 1 is blocked by decomposition education( X, Y). 7 we can be the taking direct information. 0 is an physical cylinder of A-modules. 0; and carefully in the general case. Y) we have also set girls Bringing historic elements. ExtnA( X, Y) is serial of the diabetes of a free elocution of X. Y) is an harmful universal ebook.