title: use another sparql inside sparql IN clause
body: <p>I'm using SPARQL and I wonder if I can put an sparql inside in clause?
  To be more specific, I need to get entities(s1,s2) who have specific condition for this sparql query[s1's aggregate value over a field is more than say 5]</p>
  
  <pre><code>select 
  ?s1 ?x ?s2.
  WHERE {
           {?s1 rdf:type dbpedia-owl:Scientist.}
           {?s2 rdf:type dbpedia-owl:Scientist.}
           {?s2 dbpedia-owl:field ?x.}
           {?s1 dbpedia-owl:field ?x.}
  }
  </code></pre>
  
  <p>so I need to add an extra IN clause like this</p>
  
  <pre><code>SELECT
  ?s1 ?x ?s2.
  WHERE {
        {?s1 rdf:type dbpedia-owl:Scientist.}
        {?s2 rdf:type dbpedia-owl:Scientist.}
        {?s2 dbpedia-owl:field ?x.}
        {?s1 dbpedia-owl:field ?x.}
        {?s1 IN 
              {
               SELECT  ?s1  WHERE {
                                      SELECT ?s1 (COUNT(?p) AS ?prizes) {
                                      ?s1 dbpprop:prizes ?p.
                                      } group by (?s1) 
                                   }FILTER (?prizes &gt; 2) 
               }
         }
   }
  </code></pre>
  
  <p>But I got error on the sparql query parser.....
  does anybody know how to fix it?</p>