Cosieves on may be organized into a category . For convenience we will note the domain of a sieve as a part of the data. Thus objects of are pairs of the form where and is a cosieve in . A morphism is a map such that the cosieve is a subset of . The usual composition of underlying morphisms in defines a composition in , because where . Note that .
Revised on July 11, 2009 05:22:07
by Toby Bartels