Prelude and Fugue in C Major, BWV 846 (WTC I)

J. S. Bach composed two books known as The Well-Tempered Clavier (Das Wohltemperierte Klavier).  Each of these books contains 24 pairs of preludes and fugues, in all major and minor keys.  The first book is dated from 1722, and the second one from 1742.

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).