https://en.m.wikipedia.org/wiki/Carlos_Sanchez-Gutierrez

Wiener Blut (Viennese Blood or Viennese Spirit) is an operettanamed after the “Wiener Blut” waltz, supposedly with music by the composer Johann Strauss the Younger, who did not live to witness the première. Such was the popularity of the original “Wiener Blut” Op. 354 waltz until the time of the composer’s death that his work would be chosen as the name of the operetta with libretto by Victor Léon and Leo Stein set around the Vienna Congress of 1814 to 1815.
https://en.wikipedia.org/wiki/Wiener_Blut_(operetta)

https://en.m.wikipedia.org/wiki/Circle_of_fifths

The cor anglais (UK: /ˌkɔːr ˈɒŋɡleɪ/, US: /ˌkɔːr ɑːŋˈɡleɪ/^[1][2] or original French: [kɔʁ ɑ̃ɡlɛ];^[3] plural: cors anglais) or English horn in North America, is a double-reed woodwind instrument in the oboe family. It is approximately one and a half times the length of an oboe.

Cor anglais or English horn

Woodwind instrument
Classification	Woodwind Wind Aerophone
Hornbostel–Sachs classification	422.112-71 (Double reed aerophone withkeys)
Developed	about 1720 from the oboe da caccia
Playing range
Written pitch, notated in F, sounds a perfect fifth lower Sounding pitch
Related instruments
Piccolo oboe Oboe Oboe d’amore Oboe da caccia Bass oboe Heckelphone Contrabass oboe

The cor anglais is a transposing instrument pitched in F, a perfect fifth lower than theoboe (a C instrument). This means that music for the cor anglais is written a perfect fifth higher than the instrument actually sounds. The fingering and playing technique used for the cor anglais are essentially the same as those of the oboe and oboists typically double on the cor anglais when required. The cor anglais normally lacks the lowest B♭ key found on most oboes and so its sounding range stretches from E₃ (written B♮) belowmiddle C to C₆ two octaves above middle C.

https://en.m.wikipedia.org/wiki/Cor_anglais