question: Was a person a film producer that influenced M2 and was influenced by M3 and M4
query: SELECT count(*) WHERE {
  ?x0 a ns:film.producer .
  ?x0 a ns:people.person .
  ?x0 ns:influence.influence_node.influenced M2 .
  ?x0 ns:influence.influence_node.influenced_by M3 .
  ?x0 ns:influence.influence_node.influenced_by M4
  }