Frédéric Chopin:

From September 1823 to 1826 Chopin attended the Warsaw Lyceum, where he received organ lessons from the Czech musician Wilhelm Würfel during his first year. In the autumn of 1826 he began a three-year course under the Silesian composer Józef Elsner at the Warsaw Conservatory, studying music theory, figured bass and composition.[n 3] Throughout this period he continued to compose and to give recitals in concerts and salons in Warsaw. He was engaged by the inventors of a mechanical organ, the "eolomelodicon", and on this instrument in May 1825 he performed his own improvisation and part of a concerto by Moscheles. The success of this concert led to an invitation to give a similar recital on the instrument before Tsar Alexander I, who was visiting Warsaw; the Tsar presented him with a diamond ring. At a subsequent eolomelodicon concert on 10 June 1825, Chopin performed his Rondo Op. 1. This was the first of his works to be commercially published and earned him his first mention in the foreign press, when the Leipzig Allgemeine Musikalische Zeitung praised his "wealth of musical ideas".

Please answer a question about this article. If the question is unanswerable, say "unanswerable". What was the name of the teacher of Chopin's three year course that began in the fall of 1826?
Józef Elsner