PROVINCETOWN — During an onstage discussion with Patti LuPone about the performers who have helped define the modern Broadway musical, Seth Rudetsky had a question for his guest: “Do you think of three divas: Bernadette, Betty, and Patti?’’

LuPone immediately shot back: “No, I think of one diva.’’ Then she let loose with one of her eruptive bursts of laughter.