s#sequences</A>)', is like a restriction
operation.
Should we use different notations for these two different uses? I believe
the XML namespace mechanism uses ':' for namespace prefixing and '#' for
referencing parts.

2. Is importation transitive or absorbtive or something else? For example,
consider the following situation.
    * the ontology B is located at B-place
    * the ontology C is located at C-place
    * the ontology A contains an importing expression '(imports b B-place)'
    * the ontology B c