What is the exposition of "The Lottery?"

I think that the exposition of Jackson's short story is
what adds to its horror.  The day is described as a beautiful June day.  The sun is
shining and there is a perceptible feeling of joy in the air.  Children run and scamper
around, excited at the freedom experienced with school over.  The boys are, innocently
it seems, collecting stones and stacking them, while the girls are off chatting.  The
fathers are gathered in one area, commiserating, talking to one another about crops and
such, while watching over their children.  All in all, the day is a wonderful one and
the reader has little idea as to why they are all gathered.  The exposition is spent
detailing names like "Dickie Delacroix" and the like.  Adding to this is the seemingly
harmless arrival of both Mr. Summers, who is struggling a bit with the weight of the box
and pedestal, and the tardiness of Tessie Hutchinson, along with her conversations with
her best fried, Mrs. Delacroix. The serene tranquility of the exposition belies the
horror that is to play itself out.