Flowers for Algernon
Over the years before "Nova" appeared, Delany had already won the Nebula Award twice for best science fiction novel of the year: "Babel-17" had gained the award in 1967 (in a tie for best novel of 1966 with Daniel Keyes's "Flowers for Algernon", a.k.a. "Charly"). "The Einstein Intersection" won him the award the following year in 1968 (for best novel of 1967).