We can generate the requirements and design documents from a working system at any time. The requirements document simply lists requirements grouped by domain. For each domain we have functional requirements, system properties and constraints. The design document shows which class or operation offered by a class satisfies each functional requirement. During design work a requirement may be moved between domains, but some domain must undertake to satisfy each functional requirement. System properties (e.g. the efficiency of track finding) can only be checked when the system is built; some may be attributed to a single domain though many will not. Constraints (e.g. saying which external packages to use), may be general or upon domains. The document includes Object Interaction Graphs (OIGs) for Use Cases of interest. Each Use Case appears as an explanation of the OIG. We hope to see all operations exercised by an OIG and none which appear to have no use.