Subject: Fwd: Qu. of Cruickshank Date: 12 Mar 2002 12:01:17 +0200 From: "Peter Witbooi" The following reference is not quite to the point but might just be helpful. On the question by Jim Cruickshank below, in the article, Daniel Quillen, Higher Algebraic K-theory I, in: Springer-Verlag Lecture Notes in Mathematics 341, Algebraic K-Theory I - Higher K-theories, pp85-147, the category QM, for an exact category M (p100), has composition defined in a manner dual to that of Cruickshank. Sincerely, Peter Witbooi Department of Mathematics University of the Western Cape Private Bag X17 7535 Bellville South Africa ======= Subject: question for the topology list Date: Mon, 11 Mar 2002 16:36:21 +0000 From: james cruickshank I have a question for the topology list: I have recently been thinking about the following category in connection with knot invariants: The objects are groups. A morphism G_1 --> G_2 is diagram G_1 --> H <-- G_2. Two morphisms are composed by taking pushout. I am sure that I have seen this category mentioned somewhere but I can't remember where. Can anyone supply a reference that would contain information about this category? Thanks Jim Cruickshank.