Conversation so far:
What is Tristan and serialism?
Messiaen composed the song cycle Harawi, the first of three works inspired by the legend of Tristan and Isolde.
What was the song about?
The second of these works about human (as opposed to divine) love was the result of a commission from Serge Koussevitzky.
Was he commissioned to write any other songs?
CANNOTANSWER.
Are there any other interesting aspects about this article?
Messiaen taught an analysis class at the Paris Conservatoire.

Question: How long did he teach for?
Self-contained rewrite: How long did Olivier Messiaen teach for?