We crowd around library tables, hang between book cases, balance paper plates with delicious home-cooked food while listening to White Christmas in its jazz-and-blues-garb: what else can it be but the Annual Holiday Jazz Concert and Potluck with Pat Loomis and his crew? It's the thirteenth year of it, no less. As before, John Hampton will cook his Famous Chili and a few other things, says Carol Glass, one of the library staff who happens to be married to him. And, since it's a Potluck, you can bring food to share as well. It starts at 6:30 PM, rain or shine.