anchor.diff:      ;
   
   groupClause
  -    : GROUP BY groupCondition+ -> ^(GROUPBY groupCondition+)
  +    : GROUP BY groupCondition+ -> ^(GROUP_BY groupCondition+)
       ;
       		 
   groupCondition
  
positive.code:     ;
  
  functionCall
      : iriRef argList -> ^(FUNCTION iriRef ^(ARGLIST argList))
      ;
  
  argList
  
negative.code:     ;
  
  notExistsFunction
      : NOT EXISTS groupGraphPattern -> ^(NOT_EXISTS groupGraphPattern)
      ;
  
  aggregate
  