The string quartet is generally considered as the chamber-music genre of the classical era: invented by Haydn, elaborated by Haydn and Mozart, and brought to its compositional peak by Beethoven. All later quartet composers had to measure themselves against the works of these three masters. This applies first and foremost to Mendelssohn, who has always been called a ''classical romantic.'' His Quartet in a minor op. 13 in particular is said to have strong Beethovenian stylistic traits. It was com