Structured theory presentations and logic representations

The purpose of a logical framework such as LF is to provide a language for dening logical systems suitable for use in a logic-independent proof development environment. All inferential activity in an object logic (in particular, proof search) is to be conducted in the logical framework via the representation of that logic in the framework. An important tool for controlling search in an object logic, the need for which is motivated by the diculty of reasoning about large and complex systems, is the use of structured theory presentations. In this paper a rudimentary lan-guage of structured theory presentations is presented, and the use of this structure in proof search for an arbitrary object logic is explored. The behaviour of structured theory presentations under representation in a logical framework is studied, focusing on the problem of \lifting " presentations from the object logic to the metalogic of the framework. The topic of imposing structure on logic presentations, so that logical systems may themselves be dened in a modular fashion, is also brie y considered.