Introduction. If P is a ring and M a left P-module, then homological algebra attaches three dimensions to M, projective, weak, and injective(1)By taking the supremum of one of these dimensions as M… Expand

This is the story of a teacher's campaign to improve the quality of his or her education and the response of teachers and students to that campaign.Expand

Introduction I. The Jacobian Conjecture 1. Statement of the Jacobian Problem; first observations 2. Some history of the Jacobian Conjecture 3. Faulty proofs 4. The use of stabilization and of formal… Expand

Introduction APIARY [23~, and subsequently GORENSTEIN Eg] and SAMUEL [2(r proved 9 3-~ t that if (2 is a point on a plane curve then no=2d Q, where dQ=dlmw0/ 9 Q and nQ = dim C'Q/~Q, 9 being the… Expand

Abstract A tree action ( G, X ), consisting of a group G acting on a tree X , is encoded by a ‘quotient graph of groups’ A = G ⧹⧹ X . We introduce here the appropriate notion of morphism A → A′ = G… Expand