**Date/Time**

Date(s) - 20/09/2023*5:30 pm - 6:30 pm*

**Location:** BSB 104

**Speaker:** Lothar Sebastian Krapp (University of Konstanz)

**Title:** Under construction: building mathematical objects by constructive proofs

**Abstract:** When an engineer wants to find an object with specific properties, they would build or at least design it. For a mathematician, on the other hand, it is often enough to be convinced that the nonexistence of the desired object is impossible. While in other scientific disciplines such an understanding of “existence proofs” would be quite problematic, mathematicians regularly work with abstract objects they cannot construct.

However, what makes a proof constructive? In my talk, I will present some simple examples of well-known proofs showing that even arguments that seem non-constructive at first glance can lead to a construction of the object we are looking for. Moreover, I will discuss what it means in our thinking to have constructed an abstract object such as an irrational number or an uncountable set.

Coffee available 5pm in Hamilton Hall – 216 (Lounge)

To volunteer to give a talk please visit our website: https://sites.google.com/view/casual-math-seminar/give-a-talk