this fugue from book 1 of the well tempered clavier consists of 3 voices and a subject that is revisited several times throughout the piece. (I counted about 14.) The expository statement, or the subject rather, begins the piece and lasts four measures until the next voice begins and reinstates the first motive. the second time the subject is played, it is transposed down a 5th, so the starting note is b flat and no longer f. about the 6th time the subject enters, it is inverted, as seen in measure 19 in the bass line.
the fugue also has two countersubjects that appear, the first one appearing after measure 9 anda again after measure 25.