Re: the alpha of Omega

Sorry I didn't reply sooner to this; I was enroute from Perugia to Buffalo. As I recall, the original omega was the sheaf of CLOSED sets on a topological space, in a paragraph devoted to applications to notions like sections with supports. Having recognized the importance of the subobject classifier, making the observation that isomorphic things probably would not remain notationally distinct forever, and especialy wanting not to change an "established"(!) symbol, we replaced the T (for truth) (which was used in my IAM 69 talk and ICM 70 paper). Thus the mega oh is a coincidence. Unfortunately I do not recall in which part of the prepublished SGA4 that paragraph occurs .