In the talk, first I explain how undecidability results enter topology. Then I focus on the specific case of 4-dimensional manifolds (4-dimensional analogues of surfaces). First I outline a classical approach of Markov showing that there exists an unrecognizable 4-manifold M. (There is no algorithm to decide whether another manifold on input is homeomorophic to M.) Then I sketch how one may improve this to get simpler examples.
Localisation
Salle de séminaire 4B125 (bâtiment Copernic)
5 Boulevard Descartes 77420 Champs-sur-Marne