Dijkstra: Reasoning About Programs (1990) [video]
youtube.comI'm always excited when I realize that my one semester of Discrete Math allows me to understand lectures like this!
If you are tempted to dig further into these techniques there's this book:
https://www.amazon.com/Science-Programming-Monographs-Comput...
Cool side note, introducing Prof. Dijkstra was a younger Eric Schmidt during his tenure as a software engineering manager at Sun. I wonder where all of the other lectures are? Somebody should repost them.