I've been invited to give a talk for Cafe Scientifique, 8.30pm Mon 16 March at the Edinburgh Filmhouse. Title and abstract below. I've been asked to speak without using overheads or visuals, which should be an interesting challenge! The link above takes you to the Facebook page for the event.Proofs are Programs: 19th Century Logic and 21st Century ComputingAs the 19th century drew to a close, logicians formalized an ideal notion of proof. They were driven by nothing other than an abiding interest in truth, and their proofs were as ethereal as the mind of God. Yet within decades these mathematical abstractions were realized by the hand of man, in the digital stored-program computer. How it came to be recognized that proofs and programs are the same is a story that spans a century, a chase with as many twists and turns as a thriller. At the end of the story is a principle for designing programming languages that will guide computers into the 21st century.Similar material is covered in this article