練形術
Art of training the body
煉石補天
Refine the stone to repair the innate
千錘百鍊
After hard work and numerous revisions
練, 煉 and 鍊, are all pronounced liàn. They are all made of 柬, to select, but written with different radicals*. They all can be used as to describe one's training. Even if they seem interchangeable, those three characters actually refer to different parts of training in internal arts.