anchor.diff:      ;
   
   prologue
  +    /* The tree rewriting rule, as used here, implicitely induces a sorting order */
       : (baseDecl | prefixDecl)* -> ^(PROLOGUE baseDecl* prefixDecl*)
       ;
   
   baseDecl
       : BASE IRI_REF -> ^(BASE IRI_REF)
  -    ;
  +    ; 
   
   prefixDecl
       : PREFIX PNAME_NS IRI_REF -> ^(PREFIX PNAME_NS IRI_REF)
  
positive.code:     ;
  
  brackettedExpression
      : OPEN_BRACE expression CLOSE_BRACE -> expression
      ;
  
  builtInCall
  
negative.code:     ;
      
  modify
      : (WITH iriRef)? (deleteClause insertClause? | insertClause) usingClause* WHERE groupGraphPattern -> ^(MODIFY ^(WITH iriRef)? deleteClause* insertClause* usingClause* ^(WHERE_CLAUSE groupGraphPattern))
      ;
    
  deleteClause
  