Task: Question Generation
Input (English): Chopin's études are largely in straightforward ternary form. He used them to teach his own technique of piano playing—for instance playing double thirds (Op. 25, No. 6), playing in octaves (Op. 25, No. 10), and playing repeated notes (Op. 10, No.  7).
Output (English): What pieces of his did Chopin use to teach his technique?