three Piano Quartets
... that Beethoven composed three Piano Quartets at age 15, which were published only after his death?
... that <a href="./Ludwig_van_Beethoven" id="mwBX8" rel="mw:WikiLink" title="Ludwig van Beethoven">Beethoven</a> <i id="mwBYA">(pictured)</i> composed <b id="mwBYE"><a href="./Piano_Quartets_(Beethoven)" id="mwBYI" rel="mw:WikiLink" title="Piano Quartets (Beethoven)">three Piano Quartets</a></b> at age 15, which were published only after his death?