Columbia subject headings:
Ballet--England--London--History--20th century.
Opera--England--London--20th century.
Royal Opera House (London, England)
Harvard subject headings:
Ballet--England--London.
Opera--England--London
Royal Opera House (London, England)--History.
Princeton subject headings:
Ballet--England--London.
Opera--England--London.
Royal Opera House (London, England)--History.