Section B, or “Development” follows the Exposition. It generally uses material from the Exhibition, but in a more or less radically modified way. In section A' or "Recapitulation", material A returns relatively intact. Each of these sections has a relatively complex internal model as follows: The Exhibition sets out the main thematic elements and has its own internal form as follows: 1) A primary key section which contains: a. the main or main theme that is one sentence or more and establishes the home key,