Abstract
The demonstration, at the beginning of the XXthcentury that mathematics could in principle be completely formalized had a profound impact on the way the subject has been viewed ever since. However, the emphasis of formalization has been strongly on symbolic reasoning, and much less on visual and diagrammatic reasoning, which plays a fundamental role in research, and often convinces mathematicians of the truth of a statement long before they have written a proof in symbolic form. This seminar examined the role of diagrammatic reasoning, using as a case study an article by Alain Connes and Dirk Kreimer that includes Feynman diagrams.
