Welcome to the section of the Around toposes Forum specifically devoted to basic questions about toposes, categories and related subjects.

Please note that the forum (as well as the blog) has built-in latex editors for writing mathematical formulas; just write

for each latex expression you need to insert, and it will be automatically displayed (you can check the result by clicking on the Preview button).

You can also, for a better graphical result, just type as if you were writing a normal latex source (but beware that in that case the Preview button will not show the compiled result - still, you will be able to edit your message for 60 minutes after your original submission, in particular to correct any typos or rendering mistakes). Here is an example:

$\textrm{Hom}_{ [{\cal C}^{\textrm{op}}, \textbf{Set}]}(y_{\cal C}(c), F)\cong F(c).$

We look forward to hearing from you!