Columbia subject headings:
Chevalier au cygne.
Lohengrin (Legendary character)
Swans--Folklore.
Harvard subject headings:
Chevalier au cygne.
Lohengrin (Legendary character)
Lohengrin.
Swans--Folklore
Princeton subject headings:
Chevalier au cygne.
Swan (in mythology and folk-lore)
Swan-knight (Legendary character)