Columbia subject headings:
Opera--Italy--18th century--Librettos.
Opera--Italy--19th century--Librettos.
Harvard subject headings:
Opera--Italy--18th century--Librettos.
Opera--Italy--19th century--Librettos.
Princeton subject headings:
Opera--Italy--18th century--Librettos.
Opera--Italy--19th century--Librettos.