A course on abstract interpretation [1], taught by Radhia [2] and Patrick [2] Cousot at ENS in 1989. To my shame, I must admit that I didn't appreciate it at the time.

[1]: https://en.wikipedia.org/wiki/Abstract_interpretation

[2]: https://en.wikipedia.org/wiki/Radhia_Cousot

[3]: https://en.wikipedia.org/wiki/Patrick_Cousot