Here is the screenplay - it has a title sequence over scenes and pictures of the Dupea family, including one of Robert’s recital program music: Grebner’s “Five Easy Pieces”
However that sequence wasn’t used - the movie starts on the oil rig with the titles over that. Maybe the director liked the ambiguity of “Five Easy Pieces”
The five classical pieces are:
Chopin - F Minor Fantasy
Bach - Chromatic Fantasy and Fugue
Mozart - Piano Concerto K271
Mozart - D Minor Fantasia
Chopin - Opus 28, no 4 - Prelude E Minor
The last two would be considered easy. The others are not. Bobby plays the two Chopin ones. Bobby screws 3 women in the movie. So… it doesn’t quite make sense in the movie.