Premise: Belle de Jour (] ) is a 1967 French drama film directed by Luis Buñuel and starring Catherine Deneuve, Jean Sorel, and Michel Piccoli. Based on the 1928 novel "Belle de jour" by Joseph Kessel, the film is about a young woman who spends her midweek afternoons as a high-class prostitute while her husband is at work.
Hypothesis:  Belle de jour is a film that may be based on a book.