The Exposition is followed by section B, or "Development". He usually uses material from the Exposition, but in a more or less radically modified way. In the A' or "Summary" section, the A material returns relatively intact. Each of these sections has a relatively complex internal scheme as follows: The Exposition establishes the main thematic elements and has its internal form as follows: 1) A primary key section containing: a. the main or primary theme which is a sentence or more in length and establishes the home key,