Canon (music)
Bach was a great master at writing canons and other very complicated musical forms.  After 1750 composers became less interested in writing music which was all polyphonic, although many composers still showed an interest in counterpoint.  Haydn, Mozart and Beethoven all wrote canons and even Romantic composers like Schumann and  Brahms showed an interest.  César Franck wrote a canon for the fourth movement of his Sonata for Violin and Piano.  It is quite easy to hear this canon, because the violin plays the tune an octave higher than the piano, and the piano holds on to a long note every other bar while the violin catches up.