anchor.diff:  //https://docs.oracle.com/cd/E11882_01/server.112/e41084/statements_5001.htm#SQLRF01201
   create_cluster
       : CREATE CLUSTER  cluster_name '(' (','? column_name datatype SORT?)+ ')'
  -          ((physical_attributes_clause
  -           | SIZE size_clause
  -           | TABLESPACE tablespace
  -           | INDEX
  -           | (SINGLE TABLE)? HASHKEYS UNSIGNED_INTEGER (HASH IS expression)?
  -           )+
  -          )?
  +          ( physical_attributes_clause
  +          | SIZE size_clause
  +          | TABLESPACE tablespace
  +          | INDEX
  +          | (SINGLE TABLE)? HASHKEYS UNSIGNED_INTEGER (HASH IS expression)?
  +          )*
             parallel_clause? (ROWDEPENDENCIES | NOROWDEPENDENCIES)? 
             (CACHE | NOCACHE)?
             ';'
  
positive.code: 
  //https://docs.oracle.com/cd/E11882_01/server.112/e41084/statements_1010.htm#SQLRF00805  
  alter_index
      : ALTER INDEX index_name (alter_index_ops_set1 | alter_index_ops_set2)
        ';'
      ;
  
  alter_index_ops_set1
      : (deallocate_unused_clause
        | allocate_extent_clause
        | shrink_clause
        | parallel_clause
  
negative.code: 
  modify_index_partition
      : MODIFY PARTITION partition_name
          ( modify_index_partitions_ops+
          | PARAMETERS '(' odci_parameters ')'
          | COALESCE
          | UPDATE BLOCK REFERENCES
  