FLEX-ABILITY POPS serie – 11 popular songs and evergreens in individual books for different instruments in 4-part arrangements written in the way where all the books can be mutually combined and individual parts in differents books can be interchangeable. In addition, individual parts in this arrangement are written in different difficulty level, so this quartet can be played by students with different skills. The first part (melodic) is written in level 2,5 to 3, the second part (harmonic) is written in the level 2 to 2,5, the third (harmonic) is 1,5 and the fourth (harmonic or bass line) is in difficulty level 1. You can buy an accompaniment CD. Very nice, variable and well-made serie.