question: Were M3 and M4 influenced by a film producer and influenced by a Mexican person
query: SELECT count(*) WHERE {
  ?x0 a ns:film.producer .
  ?x1 a ns:people.person .
  ?x1 ns:people.person.nationality ns:m.0b90_r .
  M3 ns:influence.influence_node.influenced_by ?x0 .
  M3 ns:influence.influence_node.influenced_by ?x1 .
  M4 ns:influence.influence_node.influenced_by ?x0 .
  M4 ns:influence.influence_node.influenced_by ?x1
  }