Mandolin 1796: Sonatine WoO 43a; Adagio ma non troppo WoO 43b; Sonatine WoO 44a and Andante con Variazioni WoO 44b. The opera "Don Giovanni" by Mozart (1787) includes mandolin parts, including the accompaniment to the famous aria "Deh vieni alla finestra", and Verdi's opera Otello calls for guzla accompaniment in the aria "Dove guardi splendono raggi", but the part is commonly performed on mandolin. Gustav Mahler used the mandolin in his Symphony No. 7, Symphony No. 8 and Das Lied von der Erde. Parts for mandolin are included in works by Schoenberg (Variations op. 31), Stravinsky (Agon), Prokofiev (Romeo and Juliet)
Mandolin suit them to Cai luong opera music. In the mid-1930s, they made concave frets, scooping out extra wood between the frets, making the space between them deep and to allow the musicians to bend the notes, and stringing them with four single strings. Musicians Hai Nén and Hai Nhành were associated with the instruments, possibly being the first to use them. The "sunken-fret mandolin" (mandolin phím lõm) did not meet the musical needs as well as the sunken-fret guitar, because the mandolin's rigidity made it painful to get the same effects from the strings. Also the mandolin's narrow fretboard made