What is the antagonist and protagonist in story lady or tiger?

The story "The Lady, or the Tiger?" by Frank R. Stockton has no clear-cut antagonist or protagonist. Antagonists are usually characters that oppose the goals of the protagonist. Protagonists are usually the main characters in a story that the audience is meant to root for. Since the story involves two unknown figures, a princess, a gentleman, and two chambers—one housing a young lady, the other a tiger—the reader does not know for certain the motivations or goals of any characters.