INSERT {
  GRAPH <A> {
    _:a a foaf:Person ;
        foaf:name "a" ;
        foaf:knows _:b .
    _:b a foaf:Person ;
        foaf:name "A_b" .
  }
  GRAPH <B> {
    _:a a foaf:Person;
        foaf:knows _:c .
    _:c a foaf:Person ;
        foaf:name "B_c" .
  }
}
