how to express the rule of SILRI?

Hi,
    Is there some handbook(or short papers) to show how to use SILRI? 
    There is only one example and a short readme. I really want more syntax information.
    For Example, Is there any native mathematic operator or founction such as >. + ,-.
    If I want to express that someone who is older than 60 is an old man, How can I express it?
    
The following rule is not right, who can help me?
    FORALL A,P old(P) <-  P["http://description.org/schema/age"->>A];greater(A,60).

   <?xml version="1.0"?>
 <rdf:RDF
   xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
   xmlns:s="http://description.org/schema/">
    <rdf:Description about="Satti">
      <s:age>70 </s:age>
    </rdf:Description>
</rdf:RDF>

Tong.