Christopher Webber wrote:

>Doubtless others will point out to Robert that the reference is to
>E.T.A.Hoffmann's through-written opera "Undine" (1816) for which La
>Motte-Fouque provided a libretto based on his own verse story.

Point taken, but, Christopher, Undine by La Motte-Fouque is prose, not
verse.

Robert Peters