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Building a System
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What Is a System?
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* Also called Application or Program or ...
* Collection of :dfn:`library units`

   - Which are a collection of packages or subprograms

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Library Units 
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* Those units not nested within another program unit
* Candidates

   - Subprograms
   - Packages

* Dependencies between library units via :ada:`with` clauses

   - What happens when two units need to depend on each other?

