Re: abstraction of notation from sets.

On Feb 23, 2010, at 4:43 PM, peasthope@shaw.ca wrote:

When S is a set, the notation "a \epsilon S" is familiar. Is this ever extended to CT? All the texts I recall use natural language such as "A is an object of C". What if a more symbolic notation is required?

I've seen $a \in Ob(C)$ numerous times, and also - though primarily from Barr & Wells - $a \in C_0$, with the rationale that a category is a graph (consisting of vertices C_0 and edges C_1), with extra conditions introduced to capture the composition operation, showing up as functions defined on composable sequences C_n of n edges (most often for n=2, or 3 for associativity). -- Mikael Vejdemo Johansson [For admin and other information see: http://www.mta.ca/~cat-dist/ ]