scribble: rules for foaf:uncle as test case for 'social meaning'

<rdf:Property rdf:about="http://xmlns.com/foaf/0.1/uncle">
  <rdfs:label>uncle</uncle>
  <rdfs:comment>An uncle of this person.
   uncle(P1,P2) if parent(P1,P3), sibling(P3,P2), gender(P2,'male')
   uncle(P1,P2) if parent(P1,P3), sibling(P3,P4), spouse(P4,P2),gender(P2,'male')
  </rdf:comment>
  <rdfs:range rdf:resource="http://xmlns.com/foaf/0.1/Person" /><!-- could have MalePerson?...-->
  <rdfs:domain rdf:resource="http://xmlns.com/foaf/0.1/Person" />
</rdf:Property>