anchor.diff:  COLLECTION;
   BLANKNODEPROPERTYLIST;
   OBJECTLIST;
  +TRIPLE;
   NOTEXISTS;
   CONDITIONAL_OR_EXPRESSION;
   CONDITIONAL_AND_EXPRESSION;
  
positive.code:     ;
  
  triplesSameSubjectPath
      : varOrTerm propertyListNotEmptyPath 
      | triplesNode propertyListPath
      ;
    
  propertyListNotEmptyPath
  
negative.code:     ;
  
  groupOrUnionGraphPattern
      : groupGraphPattern (UNION ^groupGraphPattern)*
      ;
  
  filter
  