Kurt Vonnegut (Slaughterhouse 5) and Joseph Heller (Catch-22) served together in WWII. In both books, Slaughterhouse 5 and Catch-22, each author refers to the other.
Reading Catch-22 encouraged me to pick up Slaughterhouse 5 after seeing Heller speak so respectfully of “an author he served with named Vonnegut”.