anchor.diff:  WHERE EXISTS {
   	MATCH (other:Actor)-[:ACTED_IN]->(movie)<-[:ACTED_IN]-(actor)
   	WHERE other.name = actor.name
  +  WITH other, count(*) as c
  +  WHERE c > 1
   }
   RETURN actor
   ----
  
positive.code: 
   * It has to be a read-only query. Updating the graph as part of a predicate is not allowed.
   * It cannot end in a +RETURN+ clause, nor may it contain +UNION+
   * If +WITH+ ends the subquery, it should be able to change the cardinality of the subquery in an for +EXISTS(...)+ interesting way.
  In other words, they should include +WHERE+ or +SKIP+, since they could turn a query that returns rows into one that does not.
  
  ==== Simple subquery exists
  When the subquery can be described with a single +MATCH-WHERE+ clause, the +MATCH+ keyword can be omitted.
  The difference between this form and a simple pattern predicate, which is already available is that this form allows for introducing new variables inside the +EXISTS(...)+ scope.
  
  === Examples
  _Example 1A:_
  
  Return all nodes that have a property named slogan.
  [source, cypher]
  ----
  MATCH (actor)
  WHERE EXISTS(actor.slogan)
  RETURN actor
  ----
  
  _Example 1B:_
  Return all nodes with both first name and second name:
  [source, cypher]
  ----
  MATCH (actor)
  WHERE EXISTS(actor.firstName + actor.lastName)
  RETURN actor
  ----
  
  
negative.code: === Syntax
  
  ----
  expression = <current definition of expression>
             | property exists
             | subquery exists
             | simple subquery exists
  