Compilation units (ref)
From Nemerle Homepage
A Nemerle program consists of one or more compilation units. Compilation
units are text files (conventionally with the .n extension). A
compilation unit consists of namespace-related declarations and types
within them.
The first form adds the specified namespace (which, unlike in C#,
can also be a type name) to the symbol search path. Every symbol till
end of current namespace or compilation unit (if not within namespace)
will be searched also in location specified by this path.
The second form defines an alias for a namespace or type. After using Foo = Bar.Baz; any reference to Foo.bar will be expanded to Bar.Baz.bar.
The namespace declarations puts entities defined inside it within the specified namespace. Namespaces can be nested, creating a tree of namespaces.