Invention No. 13 in A minor, BWV 784
J. S.Bach wrote 15 inventions (BWV 772-786) as exercises for his son, Wilhelm Friedemann Bach.
Invention No. 8 in F Major, BWV 779
J. S. Bach composed fifteen short pieces named inventions. These pieces are also known as two-part inventions, since they have two different lines repeat and dialogue at each other (counterpoint).