"though Petya had not the least conception of what a fugue is"

In music, a fugue is a composition which involves interweaving themes that are repeated by different instruments or voices. The word fugue is related to the Latin word fugere, to flee (as in fugitive) and to fugare, to chase; the theme is chased through the different parts of the fugue.

Listen to Buxtehude's Fugue in B flat major on Spotify.