Abstract

This paper analyzes the use of diagrams in mathematical reasoning and puts forward examples where diagrams are useful. It is not suggested that diagrammatic reasoning is sometimes necessary to justify mathematical results, but rather that such reasoning in some cases may be useful in discovering new theorems or in their communication. The topic could to a large extent have been treated by psychological research, it seems. Some typos interfere with the presentation. In the references, the title of the article and the page numbers of the article by Barwise and Etchemendy have been replaced by the information for the article by De Cruz.