Re: abstraction of notation from sets.

[Mikael Vejdemo-Johansson <mik@math.su.se>]

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


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