list.add( index );
}
if ( !list.isEmpty() ) {
final FieldIndex[] indexes = (FieldIndex[]) list.toArray( new FieldIndex[list.size()] );
LeftTupleMemory tupleMemory;
if ( conf.isIndexLeftBetaMemory() ) {
tupleMemory = new LeftTupleIndexHashTable( indexes );
} else {
tupleMemory = new LeftTupleList();
}