 There was a period of a wide variety of layouts and formal structures within first movements that gradually became expected norms of composition.The practice of Haydn and Mozart, as well as other notable composers, became increasingly influential on a generation that sought to exploit the possibilities offered by the forms that Haydn and Mozart had established in their works.In time, theory on the layout of the first movement became more and more focused on understanding the practice of Haydn, Mozart, and, later, Beethoven.