What is a ´good´ definition? Looking for the notion of a (quantum) group

Why do mathematicians need definitions? Where do they find them? And what makes a definition ´good´? We will address these questions, using as the background the historical development of the concept of a group, and much more recent, the notion of a (topological) quantum group.Adam Skalski (*1978) studied mathematics and physics in Łódź (Poland) and obtained a PhD degree in mathematics in Nottingham (UK) in 2006. He has also worked as a visiting researcher in Japan, India and France. Currently he holds a joint position between the Polish Academy of Sciences and the University of Warsaw. For his work on functionally analytic aspects of the theory of quantum groups he received the Kuratowski Prize of the Polish Mathematical Society in 2008 and the Sierpiński Prize of the Polish Academy of Sciences in 2014.