def delSyno_no_tax(connection):
    """
    Suppresses the synonyms which are not associated with any accepted taxa

    Parameters:
    -----------
    connection: psycopg2 Connection
        connection to the database
    Returns:
    --------
    List of suppressed taxon identifiers
    """
    cur=connection.cursor()
    SQL= "WITH a AS (SELECT t.cd_tax FROM taxon t LEFT JOIN taxon ta ON t.cd_syno=ta.cd_tax WHERE t.status='SYNONYM' AND ta.cd_tax IS NULL) DELETE FROM taxon WHERE cd_tax IN (SELECT cd_tax FROM a) RETURNING cd_tax"
    cur.execute(SQL)
    res=cur.fetchall()
    deleted=[r[0] for r in res]
    cur.close()
    connection.commit()
    return deleted