 Beer 's first keyboard instructor was Franz <unk> , a pupil of Johann Georg <unk> and a favoured teacher at the Berlin court . Beer also became one of <unk> <unk> 's pupils while <unk> was in Berlin . The boy made his public debut in 1801 playing Mozart 's D minor Piano Concerto in Berlin . The <unk> <unk> Zeitung reported : ' The amazing keyboard playing of young <unk> ( a Jewish lad of 9 ) , who carried off the difficult passages and other solo parts with <unk> , and has fine powers of rendition even more rarely found in one of his age , made the concert even more interesting ' . 
