Which story most likely a work of postmodern literature?

Breakfast of Champions by Kurt Vonnegut which was published in 1973 is a postmodern literature. The story is set in a make-believe town in Midland City, Ohio. The main characters Kilgore Trout and Dwayne Hoover met when Kilgore Trout travelled to Midland City to deliver a keynote address at the local arts festival. The novel deals with the subject of free will, suicide, mental illness and sadism.