NDF_ANNUL( INDF, STATUS )
-- Annul an NDF identifier
NDF_BASE( INDF1, INDF2, STATUS )
-- Obtain an identifier for a base NDF
NDF_BEGIN
-- Begin a new NDF context
NDF_CLONE( INDF1, INDF2, STATUS )
-- Clone an NDF identifier
NDF_END( STATUS )
-- End the current NDF context
NDF_VALID( INDF, VALID, STATUS )
-- Determine whether an NDF identifier is valid