Re: the alpha of Omega

On Mon, 27 Aug 2001, Keith Harbaugh wrote:

While the topic of topos subobject classifier is current, how far back can the historical and conceptual origins of the use of "$\Omega$" as the symbol denoting such be traced?

Regards, Keith Harbaugh

I seem to recall being told that it occurs somewhere in the original (mimeographed) version of SGA4 (as an interesting example of a sheaf on a site), and that Lawvere and Tierney borrowed the notation that Grothendieck et al. had used for it. However, I've never been able to find it there myself; I'm pretty sure it's not in the revised version published in Springer Lecture Notes. Peter Johnstone